Bust the Gangs: At the beginning of the game, choose a team ability. Modify Gangbuster's attack value by +1 for each KO'd opposing character possessing that team ability.

Can Gangbuster choose an Additional Team Ability (ATA), like League of Assassins or Green Lantern Honor Guard?
Yes. ATAs are still team abilities possessed by the characters.

Does Gangbuster gain the modifier if a wild card is using the selected TA?
No. Say you've chosen Batman Enemy as your TA. Joker and Two-Face possess this selected TA, but Deathstroke does not possess the TA even if he uses his Calculator TA to "copy" Batman Enemy. So Gangbuster would only have a +2 to his attack value (from Joker and Two-Face and not Deathstroke).