If you're telling your skip level something that you haven't or wouldn't tell your direct manager, that is an indication that you are failing to communicate with your direct manager. That in itself is worth the skip level person knowing.

For this is less about being careful, and more about not going off on a spontaneous rant, which honestly, isn't a good idea to do for the chain of command anyway. Spontaneous rants are for your peers. Deliberate communication up and down the COF.

My two cents anyway.