All aircraft belong to the Imperial navy though. Vendetta's being little more than Valkyrie variants fall under their jurisdiction as well. The guard use them yes but they are more 'on loan' from the navy than actually part of the Guard. But ya I guess the guard would train its own pilots for these things without having to rely on the navy. 

But I am willing to make A guardsman pilot and am trying to make a versatile character I just think it might be a little unreasonable to have the skills to pilot, and drive any vehicle in the Imperial Arsenal. usually those people are exclusive to their little skill sets. In my mind at least.