Reactive Stealth: If you have any cover or concealment when you make an initiative check, you can make a Stealth check.
Our group has a bard gnome that usually starts combat behind the front line characters. Since a character's companions provide cover, does this allow a gnome to make a Stealth check to become hidden at the start of combat?
First, we need to look at the rules for cover:
Cover (-2 Penalty to Attack Rolls): The target is around a corner or protected by terrain. For example, the target might be in the same square as a small tree, obscured by a small pillar or a large piece of furniture, or behind a low wall.
And creatures and cover:
Creatures and Cover: When you make a ranged attack against an enemy and other enemies are in the way, your target has cover. Your allies never grant cover to your enemies, and neither allies nor enemies give cover against melee, close, or area attacks.
From this, as allies only provide cover for ranged attacks, not for everything, as proper cover does, there is a strong suggestion that allies do not provide sufficient cover for stealth in this instance. Even the feat "Killer in the crowd" does not suggest sufficient cover from some enemies to provide cover for hide.
In a practical note, as this would necessitate calculating sight-lines from all enemies to the gnome, the gnome would only be able to hide from some enemies using this trick, and it would severely complicate the start of combat.
Therefore, as allies only provide cover against ranged attacks (and not, for example, melee attacks with reach) and the complexities involved in determining cover at start of combat, my answer is: "Allies alone do not provide sufficient cover for reactive stealth."
My recommendation is to carry an enshrouding candle, as a level 7 item it is a great portable source of unlimited concealment.
There have been many discussions on this topic: here(2008), here(2008), here5, here(2009) and here(2010). There is no consensus, and the stealth rules have been changed often enough to obsolete the earlier threads. This is something that you should ask your DM about.
I would say yes.
According to the compendium rules for determining cover DDI, an enemy can provide cover for another enemy against you.
If one or two of those lines are blocked by an obstacle or an enemy, the target has cover.
Ergo, your allies can provide you cover against your enemies.
I believe the default assumption in DnD is that allies never grant cover for the purposes of stealth, even when the wording is "any" cover. I base my RAI interpretation on the Assassin class, which has a class feature that's worded something like, from memory, "Allies grant cover to you for the purposes of stealth."
It feels like it would step on the class to then allow that ability to anything which does not explicitly state that they're breaking that default assumption.
After just seeing a reference to Cunning Sneak in the Rogue class description [ddi], I think they can ...
Cunning Sneak You don’t take a penalty to Stealth checks for moving more than 2 squares, and you take a –5 penalty instead of a -10 penalty to Stealth checks for running.
If you end your movement at least 3 squares away from your starting position, you can make a Stealth check to become hidden if you have any concealment or any cover, except for cover provided by intervening allies.
Bold is my highlight
Let me share my thoughts on this quandry regarding allies and cover. The DM is ultimately the deciding factor regardless of your rules interpretation, but:
*Regarding the original question going from general to specific:
Cover in general can apply to any kind of attack, but cover from creatures applies only in the instance of ranged attacks, and to no other attacks, per the compendium entry.
However the wording for Reactive stealth indicates that "any cover" satisfies the requirement for the power. Thus, if you could make a case for any kind of cover (partial or full), for any kind of theoretical attack (melee, ranged, close, area), it should work.
If the enemy were to make a ranged attack on you, you would have cover against that enemy's attack, thus you have any type of cover, and could use the gnomes reactive stealth ability by the strict reasoning above.
A) Companions of the player are creatures that are allies to the player.
B) In the eyes of the attacking creature, your ally (an enemy to attacker) is interfering with the shot of another enemy (you).
C) The compendium entry for creatures and cover applies for ranged attacks: "When you make a ranged attack against an enemy and other enemies are in the way, your target has cover." By extrapolation - I assume that this entry applies to when any creature makes a ranged attack against an enemy of that creature, not just for players.
D) Therefore, if your companion is positioned such that it interferes with any ranged shot on you from any enemy, you have "cover" as it would apply to the reactive stealth feature.
That being said, it does not make sense in real world terms in all possible cases, even with "suspension of disbelief." DM judgement would really have to apply, and if I were DM, I would reward a good roleplaying / theatrical justification. However, if the gnome were in the middle of a well lit room with his owl companion and his friends, and a dragon spotted his group, hiding behind a flying owl would not make sense to allow the gnome to hide!
*Regarding the Reference to Cunning sneak, "except for cover provided by intervening allies," for clarification, I believe that it should be noted that there are at least 3 circumustances that provide cover:
physical barriers can provide cover
creatures can provide cover for ranged attacks only in specific situations (details above)
powers and abilities of you and your allies can grant cover (example: Massive Companion level 2 shaman utility power)
The question asked by the OP refers to whether the creature companion could provide cover in the context of physical cover. Because allies can grant cover through both physical means and through powers, the quoted clause from the cunning sneak text cannot provide direct evidence to support the claim of the OP that allies can create cover by physical means.
Cunning sneak says that "allies can provide cover," but it does not say that allies can create cover by physical means through inference in all cases. As I mentioned above, allies can provide cover through other means than direct physical interference with an enemy's attack.
