I have a few different variations on the "privateer" idea running around. Basicly a fast ship with the smallest weapon I can find loaded up with engines and a bit of life support. Depending on the game, I use either a cargo ship hull, or a medium/large hull, since an actual combat ship can take out the odd solo fighter it finds as well as the unarmed ships. However, I've started seeing them escort transports now, and there have been a couple nasty suprises lately where I sent my privateer to attack their troop transport icon in the strategic view, only to find out it had escorts that ate my ship for lunch. Judging from the recent patch notes, it might be something fairly new, or it might be my difficulty level (I'm working on painful now), but the AI has learned how to escort its transports, at least some of the time.