It doesn’t show a specific type of card that it counteracts, but the wording is “Cancel any single game action in which another player is stealing a Keeper you have on the table, and instead you steal one of their Keepers.”
A: In fact, special Keeper powers that let someone take one of your Keepers is exactly the kind of situation that It’s A Trap was designed to counter. The wording is deliberately not specific to a type of card so that It’s A Trap can prevent ANY situation in which some other player may be trying to take your Keeper, whether that originates from an Action card or not.
I have often deliberately put out tempting crew members when I had It’s A Trap hiding in my hand, in the hopes that the person with The Captain would try to steal them, and I’d get to Trap their Captain instead. Or put out the Energy Crystals to try to trap the Scientist, for example.
Also keep in mind that most things which you can use It’s A Trap! to counter also can trigger You Can’t Take This Guy From Me (in Firefly Fluxx).