On my Federation-allied Romulan character, I am unable to use allied bridge officers to train skills to my commissioned bridge officers.
When I click on them to open up the dialog that should allow me to have them either train or join my crew... I only get "Join" or the option to cancel.
This is pretty major roadblock to optimizing one's bridge crew, save for common romulan officers and the bridge officers you obtain on level up (whom are few, some directly commissioned, and some from your allied faction).
Found a good trill tactical officer with Beam Overload 3? You can't train it to your existing characters. Want to have that Jem'hadar from the 4028 prison mission train someone other than Tovan with Torpedo Spread III? You can't. Do you happen to have found a Boff with Attack Pattern Omega 3 you could've taught to one of your bridge crew? You can't.
I heartily recommend this be attended to before launch.
Ayana Yirin, U.S.S. Sedna, Reconnaissance Science Vessel