Hi David, my take on the weather problems at Gib is more wind than fog after chatting to a number of flight deck crews when using the airport. With the relatively cool Atlantic meeting the relatively warm Mediterranean that is where the problems with fog arise but it is the wind swerling round the rock which causes the unstable air on final approach.
Monarch and BA was/is Captains only but after chatting to a very experienced easyJet Captain (once flew for Sabre Airways) it is Captain's only for both take off and landing. Having used Gib many times only had one divert which was actually tech with the replacement aircraft operating to Malaga as the crew did not have enough experience of operating into Gib. Maybe I have been lucky. Hope this helps.