The writer mentioned that a few characters were kept off the cover as a surprise. (I'll try and find the tweet again.) That suggests they're fellow prisoners, not enemies. If Angel rebelled against Nate, that's where he'd likely be. I'm sure there will be lots of characters we haven't seen yet, but I think most of them will be antagonists, not core members.
ETA: https://twitter.com/definitelyvita/s...326600704?s=19