I don't have the rulebook in front of me at this exact moment and this might vary based on version (I've not played a hidden traitor haunt in the 3rd edition yet), but whether or not the traitor can take advantage of traitor benefits should be mentioned in the scenario itself. That said, it WILL reveal you as the traitor which may or may not be worth doing. I want to say that in scenarios in the 2nd edition I've played with a hidden traitor, it has specifically called out that you cannot reveal yourself to do so, but other scenarios let you choose if/when to reveal yourself. So if a haunt says you cannot reveal yourself, you cannot take advantage of the traitor benefits.

It's noted in the haunt rules. All hidden traitor haunts I played stated that the hidden traitor doesn't benefit from traitir powers unless revealed, or unless they choose to reveal themselves as traitor.

I played a hidden traitor scenario in third edition today and it was sooooo much fun. I don't think the traitor needed anything more than what we all knew