Standard policies cover snorkelling. They frequently do not cover quad bikes or diving.
A hotel guide who tells you your insurance does not cover third-party excursion operators is misinformed or selling something: your travel insurance is valid throughout Egypt, and any licensed operator carries its own passenger liability — it could not obtain a tour permit otherwise.

What is worth checking is the activity list in your own policy. Snorkelling is almost always included. Scuba diving is frequently excluded above a certain depth or without a specific add-on. Quad bikes and buggies are excluded by a great many standard policies, sometimes under "motorised off-road vehicles", and that exclusion is the one people discover at the worst moment.
For divers specifically: check whether the policy covers hyperbaric chamber treatment and evacuation. Egypt has good chambers in Hurghada and Sharm, but the cost without cover is substantial. Dedicated dive insurance is inexpensive and worth it for anything beyond an intro dive.


Keep a photograph of your policy number and the emergency line on your phone, and note that hotel doctors and private clinics generally expect payment at the time and a claim afterwards.
Keep a photograph of your policy number and the emergency line on your phone, and note that hotel doctors and private clinics generally expect payment at the time and a claim afterwards.

