Can I expect a border control diver appear from behind one of the toilets at Yolanda with a water proof passport stamp.
Yes, sometimes you can expect it. Last time I was on a Safari, the boat was stopped by Egyptian coast guard ship and we were boarded by some officers. The captain asked to produce lots of papers (I guess it's licenses, insurance etc.), and all our passports were inspected.
Then there was some unidirectional exchange of cigarette packets (guess in which direction
) and off they went.
We were also inspected by coast guard on the way to St Johns a few years ago.
So yes, I guess it is a matter of luck, once in so many times but I don't think it is going to be pleasant to get caught on such routine check without the proper papers / Visa...
On land, it's 100% guaranteed that one is going to be checked for the Egyptian visa on several checkpoints along major roads that cross the imaginary line Sharm-St. Catherine. Thus, the Egyptian Visa is required not only to RasMo but also to any other place south of Sharm and/or west of St. Catherine.
So, if the boat passes the imaginary line south of Sharm- Visa. East to Tiran- no problem
The other Visa I think can be called "Sinai Coast Visa" and is valid only on eastern shore Taba-Sharm + St. Catherine.