I reckon the nature of emergency engineering problems sorta makes a hologram a really bad choice as a helper. Power fluctuations could make the hologram appear/disappear. Imagine having a holographic engineer who shorts out and drops a plasma torch in a warp core or something.
Good point, I still think it wouldn't be a bad idea as a option, especially on ships that have fully equipped holoprojectors anyway, but it'd need some damn strict safety features.
Though the obvious answer is robots. I often wondered why a society that can create Data how there were never anything less than. Like Star Wars' droids. From a real world perspective I realise I just answered my own question, it'd be stealing/not unique. But I'm not looking for C-3PO/R2-D2 main characters. Just in the background to acknowledge it's possible.