Depends on situation. For fair in-game reasons, such as drug busts, bank robberies, prison breaks, there should be a re-spawn limit....HOWEVER, one should keep in mind:
- If a gang takes over a populated area, the cops are usually the only people who are willing to, and have the duty to, get them the hell out of there. Especially if the gang causes trouble (runs around killing randoms)
- If the cops are severely out-numbered, (more than double rebel-cop ratio in a situation) then I'd say they should be able to re-spawn more. High numbers shouldn't guarantee an easy trip.
- Might be some other gray areas, but it's been too long since I played cop to understand what other situations may warrant more re-spawns.