Challenge Rating isn't the same as Encounter Level
To clarify, creatures, traps, some events (like an avalanche), and occasionally other things have a Challenge Rating (CR). When the PCs encounter something with a CR, that encounter has an Encounter Level (EL). CR is used to determine EL. (CR is also used to determine the XP earned for overcoming that challenge and any treasure the challenge may provide.)
Poachers!
As presented, the encounter is an easily overcome face-to-face rumble for most parties of four level 5 characters. As your question and Ols's excellent answer demonstrates, the math works out to the question's encounter being about EL 6.1 However, my concern is that this question approaches encounter design precisely backward.
That's not a negative criticism per se, by the way. Designing an encounter the way the question describes and reverse engineering its EL based on Table 3–1: Encounter Numbers (DMG 49) works, but at low levels especially it's a difficult calculation to make—and it need not be if approached differently.
Instead of first picking what creatures are involved in the encounter then trying to determine the encounter's EL, I suggest that the DM take the easier, more convenient path of first picking the EL then determining the Challenge Ratings of the creatures involved. That is, use to use Table 3–1 for designing encounters rather than determining the results of already designed encounters. Here are some examples.
Comparing the EL 5 encounter…
The DM can use one Challenge Rating (CR) 4, 5, 6 creature; two CR 3 creatures; three CR 2 creatures; four CR 1 or 2 creatures (at least one of whom should be CR 1); five or six CR 1 creatures; from seven to twelve CR 1/2 creatures; or one CR 4 creature and one CR 2 creature. So, to make this EL 5 encounter similar to the one you've described, one possible group of foes would be as follows:
Group A
- 1 human Ftr2 (CR 2)
- 1 human Rgr2 (CR 2)
- 1 human War3 (CR 2)
- 1 human War2 (CR 1)
Alternatively, the possible group of foes is as follows:
Group B
- 1 human Ftr1 (CR 1)
- 1 human Rgr1 (CR 1)
- 4 human War2s (CR 1)
…and the EL 6 encounter
The Dungeon Master's Guide says about 15% of encounters can be very difficult, by which it means an encounter's EL is from 1 to 4 higher than the party's average level. It also says that an EL 6 encounter can be with one CR 5, 6, or 7 creature; two CR 4 creatures; three CR 3 creatures; four CR 2 creatures; five or six CR 1 or 2 creatures (at least one of whom should be CR 1); seven to nine CR 1 creatures; from ten to twelve CR 1/2 creatures; or one CR 5 creature and one CR 3 creature. Below is one possible group:
Group C
- 1 human Ftr2 (CR 2)
- 1 human Rgr2 (CR 2)
- 3 human War3s (CR 2 each)
- 1 human War2 (CR 1)
Alternatively, this is also an EL 6 encounter:
Group D
- 1 human Ftr1 (CR 1)
- 1 human Rgr1 (CR 1)
- 7 human War2s (CR 1 each)
Group C looks closest to what was originally imagined, and this DM recommends that group be used for this boss fight.
"What about the dogs?"
This DM excluded the dogs because this DM believes a riding dog (PH 129, 131) (150 gp; creature) or a guard dog (PH 129) (25 gp; creature)—like animated dead, a mount, or even a golem—when directly controlled by the NPC should have its price subtracted from its NPC's gear value instead of adding itself independently to the encounter's EL, much like a pet or any bought or created minion's price is typically subtracted from a PC's wealth. The DM is allowed to make reasonable judgments about a creature's wealth, and warriors buying dogs is reasonable. However, a DM that has a War2 spend his entire gear value solely on guard dogs—that's eighty freakin' dogs!—is, in this DM's opinion, making an unreasonable choice.
Alternatively, if the intelligent NPCs encountered and befriended a group of wild dogs (maybe via the ranger's extraordinary ability wild empathy?) that now fights alongside the NPCs without input and direction from the NPCs, those dogs' CRs would count toward the encounter's EL.2
Gearing up
While some of the difficulty of this encounter (no matter the group's EL or its exact composition) will hinge on the foes' tactics (clearing the area of brush, for example, if they're aware of a druid's entangle spell), an equal amount of the difficulty will depend on the creatures' gear. If each NPC War2 or higher has spent its NPC gear value of 2,000 gp (DMG 127) on full plate armor (PH 123, 124) (1,500 gp; 50 lbs.); a masterwork greataxe (PH 117, 118) (320 gp; 12 lbs.); potions of beastland ferocity (Spell Compendium 29), kuo-toa skin (Stormwrack 118), or resurgence (SpC 174-5); and other appropriate incidental gear like a guard dog, some thrown weapons (including free clubs—projectile weapons other than slings and rocks likely being beyond what they can now afford), and some splash weapons, each could be a real danger.
However, the encounter may just be a sad, little speedbump if each NPC War2 or higher is kitted out poorly. ("Because clubs, a quarterstaff, a sling and rocks, and mud armor are free, I spent my 2,000 gp on five tons of cheese!")3
Also, there's a pretty significant difference between an NPC with 3 10s and 3 11s in its ability scores and an NPC that has an appropriately juggled nonelite array. Use that power wisely.
Final thoughts
Designing encounters appropriate for low-level PCs is an exercise in balancing, on one side, a reasonable challenge with, on the other, Oops, the bear eats everyone, and the best encounters are those the DM knows will provide the party with a reasonable challenge no matter the creatures' CRs or the encounter's mathematical EL. If, for example, the DM knows that Orcus will be a fun and reasonable encounter for that DM's party of level 1 PCs, then Orcus is, regardless of what the book says.4
Lastly, keep in mind that EL is largely only a tool for the DM; for example, XP and treasure—the typical encounter's outcomes—remain based on the encountered creatures' CRs.
1 An alternative is to compute the EL as follows: ([1 CR 2 Ftr2 +1 CR2 Rgr2 + (4 CR 1/2 War1s = CR 2) = effective CR 4] + [1 CR 1 riding dog + (3 CR 1/3 dogs = CR 1) = effective CR 2] = EL 5), and there's probably a dozen other methods besides. As described, the encounter's around EL 5 or EL 6, and that's close enough.
2 This DM would have such animals behave like wild animals, though, and this DM has most wild animals flee after being hit once then defend themselves only if cornered or protecting offspring, so they'd likely not be much of a threat. Another more zoologically-inclined DM's animals may behave differently.
3 I kid you not: there really is mud armor (Races of Faerûn 157) (0 gp; 8 lbs. of Ew!).
4 However, it usually is inappropriate for level 1 PCs to encounter Orcus. Just sayin'.