Both Grim Serv' and No Mercy use the term 'damage roll' but does that mean each dice rolled or the entire roll?
It means the entire roll.
To quote the rule book (Chapter 3: Combat)
After a successful close combat or ranged hit, the attacker rolls damage. Ranged weapons do fixed damage as listed in the Gear section. Most pistols, for example, cause 2d6 damage.
Hand weapons cause damage equal to the attacker’s Strength die plus a second die, which depends on the weapon. A barbarian with a d12 Strength and a long sword (d8 damage) rolls d12+d8 damage. Even though Strength is used to determine melee damage, this isn’t a Trait roll. Wild Cards don’t add a Wild Die to the roll and they can’t spend Bennies if they’re unhappy with the results.
All damage rolls can Ace.
►►Unarmed Combat Damage: An unarmed combatant rolls only his Strength die.
►►Bonus Damage: Well-placed attacks are more likely to hit vital areas, and so do more damage. If your hero gets a raise on his attack roll (regardless of how many raises), he adds +1d6 to the final total. This roll may also Ace!
And then we go to the extended combat example at the end of the chapter for further clarity.
Private Dan’– Joker
Dan whips out a grenade and places the Medium Burst Template directly over three of the zombies. They’re in Short Range so there are no penalties to the roll. The Joker gives him a +2 and his Throwing is d6. He rolls a 6, which is an Ace. He rolls again and gets a 4. That’s 6+4+2 for the Joker, or 12. He hits with a raise over the standard TN of 4. Grenades cause 3d6 damage, and 4d6 with the raise. After Acing and adding all the dice together, he gets a 23. That’s far more than a raise over the zombies’ Toughness 7, so that’s a wound to each. They’re Extras so that’s all they can take and all three are wiped out.
Remember the tag line: Fast, Furious, Fun! Adding +1 to each die is not fast, and being on the other end of that kind of damage isn't fun either. If you can read a rule one of two ways, one way is slow and the other way is faster, the faster method is usually the correct interpretation.
Finally, you can get official answers from Pinnacle on their forums.