A: After some discussion, we decided that Exchanging Keepers does not count as “Stealing” a Keeper.
Think of it this way: you cannot then reverse the action against your opponent. (What would that mean “and instead you [Exchange] one of their Keepers”? – that doesn’t really make sense.) So we concluded that Exchange is unstopped by It’s A Trap! Neither would you be able to use You Can’t Take This Guy From Me (a Surprise in Firefly Fluxx which has the same trigger as It’s A Trap).
What It’s A Trap! was designed to protect you against, in addition to Steal A Keeper, is any of those annoying other Keepers, like the Captain and the Scientist who can steal certain Keepers at will. One of my favorite things is to put out a juicy Crew Member and wait for the person with the Captain to try to take it, at which point, instead… It’s A Trap! and I get to steal their Captain instead!