I think they should have Crime Syndicate be played by the same people who play the JL since they're a mirror of them.
The majority of the CSA members while having similar powers are not identical doppelgangers.
It get's confusing due to the various incarnations.
The latest round they more or less were the dupes of some league members.
Ultra Man, Power Ring, Quick(possibly he had a different first name though), and possibly Seaking.
But before that none them were.
Ultraman - Human from earth
Superwoman - While an Amazon, it wasn't Diana.
Power Ring - Different man.
Owlman - Has always been Thomas Wayne jr.
Beyond that the roster changes to reflect the current league they fight.
So they would need to cast each member. Which is also for the best because then they don't need to replace faces during fights.