[@Ambiguity]

I think that the remnants of Blackwatch (Gabriel Reyes and Jesse McCree, namely) would likely be called upon by Talon to be in the task force. Hell, Gabriel could have easily jumped ship to Talon when the omnic crisis in our RP forced Overwatch into splitting apart. I know in McCree's comic he says that Talon was using some of Blackwatch's strategies, so it's known that the agents that were in Blackwatch had no trouble switching over to doing the evil that is Talon.

I know our RP isn't canon, but it does make sense in the universe for Blackwatch agents to align themselves with Talon. McCree, however, values himself as more of a bounty hunter/vigilante justice kind of guy as opposed to a cold and calculated killer like Gabriel.

All in all, it's kind of an "I really hate you but we have the same objective" kind of situation.