I think a mix of Cadians and Catachans would work best, as well as chaos-y bitz like the possessed, or spawn maybe. Zombies would also work well.
Could you specify how renegade these renegades are?
Are they just traitor guard, in which case Cadians with some rust/boils/burn marks on the armour, and then spikes and chains would suffice. Or are they full on plague-ridden-lasgun-toting-renegades, then I'd use flagellent, zombie, marauder bitz as well as quite a bit of gs.
Cheers