Your Raider's Camp is the card targeting your Heroes (as Aggie stated) so it would release them as normal. He is also correct that it would stop your opponent from rescuing a captured Hero.
An interesting point of note is that if your opponent had Heroes in his RC and you attacked with a Hero with Roman Spear, it would protect the characters from being released. However, that is a good thing for you, since if the Heroes are not released, the rescue cannot have the instead applied, so you would wind up rescuing a Lost Soul.
