Are orcas peaceful

If you mean with humans, yes. They may try to attack many other kinds of sea animals, but are friendly with humans until you stop feeding them!
They are naturally friendly, but not as friendly as dolphins. You could go up to a pack of wild dolphins and swim with them and be fine, but not wild orca's, they'd eat you or toss you around using you as a toy. The wild ones are pretty dangerous if you're in the water with them. The trained orca's are much friendlier compared to the wild ones because since they're raised in captivity they are accustomed to people. Their instincts are similar and yet very different. The wild ones have the instinct to attack and eat, the trained orca's build trust with their trainers and they don't have as strong of an instinct as the wild ones but it's still there. Yet they are very friendly once you build trust with them. But don't go out and try to swim with wild orca's if you'd like to live, it's not like Free Willy.