I just came back from my first Egyptian liveaboard, and tipping was a subject of much conversation on the boat.
On our boat, we were asked by the staff to put our tips into separate envelopes: one for the divemasters, and one for the staff.
My trip had cost about $1,000, and I tipped $150, which went $30 for the divemaster, and $120 for the staff. I set that tip level purely based on what seemed fair/just in a totally subjective sense.
The envelopes were opened by one of the divemasters and a non-diving crew member, who counted the money together. There would have been massive opportunities for scamming if the two of them agreed to do so, but I imagine that potentially incurring the wrath of their fellow crew, with whom they have to share such close quarters, would have been something of a deterrent.
My impression was that most people on the boat tipped less than I did. While I am usually quite cheap/miserly, I felt that the non-diving crew had really earned their tips, and in fact I gave a couple of them individually an extra $10 in Egyptian currency that I knew I would have little use for, as it was my last day -- and they were thrilled to get it.
Many of my fellow divers and I felt that the dive guides should not be getting their own envelopes, as they did not work any harder than a lot of the other crew, and they got to dive, eat with the guests, and generally hang out as if they were paying guests. But I tipped $30 for the divemaster mainly out of gratitude that the divemaster let me dive unguided on most dives, and gave me space and time as a photographer to do my own thing.
Egypt liveaboards are extraordinarily cheap, and I enjoyed tipping generously relative to the prices being paid. I don't think there are any hard and fast rules. It's really between you, your conscience, and your wallet.