I don't mind the slight late-registration myself, in terms of 15 minute rounds, to a maximum of somewhere around 4. I see tournaments that have late registration for 3000 chips when the blinds are 400/800. Don't like that at all, as it just causes too many people to be going all-in crazy to get a lot of chips quickly (especially in an unlimited rebuy).
Overall, I'm not a big fan of rebuy/addon but it can be used to your advantage at times. There's a lot of MTT on most main sites (PartyPoker, PokerStars
, FullTilt) that don't allow rebuys or addons - perhaps even some left without late registration.
A lot of my play is limited to MTT as there can easily be collusion on the net. If you feel it's out there so clearly - report it to the site and find yourself a new table quickly.