I don't think any of them except for Apollo and Midnighter are supposed to be specifically represenative of any pre-existing character. The fact that Swift has wings is just that....she has wings. Jack Hawksmoor is one of the most original characters I've ever seen in a comic. You simply can't compare his abilties (to communicate and talk to cities/suburban natural habitat) to any other character in comics.
If nothing else, I imagine Ellis was trying to go for an archetypical approach with the rest of the team. The Doctor, a mega-powerful modern shaman, would represent all the magic users (i.e. Doctor Fate, Doctor Strange, etc.). Engineer is Iron Man mixed with Green Lantern and taken to the next level. Hawksmoor and Jenny seem to be wholly original concepts...
