Considering the feds they were working with weren't really the good guys and cleared all their records, and they manage to boost a shit ton of money, i think trevor doesnt mind. I'm sure the way trevor sees it, he can use it to his advantage, nab tons of cash, root out any competition in his meth business. Franklin is trying to get out of the whole gang lifestyle, so him working with the feds doesn't suprise me, because if one thing is very clear in the GTA universe, in all of them, is that money makes the world go round, and, being able to boost millions upon millions and getting away with it simply because the feds need you to clean up their dirty work, doesn't sound too bad to me.