A group of South African divers is praying for your friends to be safe. Please keep us informed of any progress in the search.
Regarding the "float" and SMB, in an instance such as this an SMB would probably be useless. The guide will probably only deploy the SMB at the end of the dive and in a strong current, the dive group could be very far away from the boat by the time the SMB is deployed.
On the South African coast I've never done a dive where a "float" was not used. We call it a "buoy line". A float is attached to a reel of nylon cord that is in turn attached to the DM. As the DM descends the line peels off the reel and the skipper is able to follow the float on the entire dive. I went on a "big blue" dive in Mocambique 2 days after the tsunami in 2004 and we travelled 3 kilometres underwater in approximately 50 minutes. Without a float, the skipper would not have been able to follow us and I tremble when I think we would have surfaced 3 kilometres further out to sea with no boat or land in sight.
Perhaps some the dive operators in the Red Sea will learn from this experience (apologies if I'm sounding harsh). If diving in strong currents, ALWAYS use a float attached to the DM/guide. I'm planning a trip to the Red Sea next year and will definitely be taking my buoy line with me!!