well, right now, duck knows he's in over his head. He's gonna need a team to find those girls and get em out in one piece. So, this team ain't EXACTLY on the same job as him, it's gathering info on the same group he needs to gather info on, so it's close enough. The goals of the team will probably stay in line with his own goals for the foreseeable future, so it shouldn't be a problem. And if it becomes one, well, he's the one behind the wheel in a very literal sense. Not to mention he could USE the money.
As for taking out the gang leader, Duck is willing to play along for now, but he aint no hitman. If this dude NEEDS to get taken out, those types of things have a way of happening on their own, and if it happens, duck aint gonna sneeze at extra money. Not to mention, who the fuck is behind Andy and who's behind the mongrels? Duck knows enough about the world to know people are often duped into working against their own long term best interests in exchange for a temporary leg up on today's problems. He doesn't intend to be one of those duped.