The OP asked if anyone had evidence of such an event in 'real life'. As we all know anything is possible in this sim with or without the various uber-mods, no matter how improbable in the real world. We can always reload a saved game, they couldn't...
My answer to the question as posted is 'No, there is no evidence'. In 40+ years of reading about U-Boats I've never heard of such a thing. Given the limitations of the deck gun itself and the lack of time-fused ammunition it would be unlikely any RL U-Boat even tried it.
If any boat had succeeded in using it's DG to down an aircraft and made it back to port, the Nazi propaganda machine would have had a field day. The fact that that never happened is one clue there was no such recorded event.
Reservation: The only possibility that remains are the few remaining U-Boats 'lost to unknown causes' that may also involve missing aircraft at about the same time and place. So we'll never know for sure.
Now, if you will excuse me, I have to reload my save where I'm out of torpedoes and trying to sink HMS Nelson by ramming...
