I work on sailing ships, where there are only two people working, the employer and myself.
So yes, I always tell my skipper.
I'm very good at preventing hypos during sailing, but you never know, and I want my skipper to know what to expect if I make a mistake. We also usually eat with the (paying) guests, so I want both my employer and our guests to know why I'm not always eating with them, I don't want to look rude.
Currently I'm doing technical work on a ship to prepare it for the sailing season, so no guests, just my employer and I, and sometimes a specialist on electricity or wood or steel work.
I didn't feel the need to disclose, but my diabetes was pretty clear when I injected for lunch, I didn't feel the need to hide it either. Turns out he has diabetes as well.