Gib is open to GA, I've seen GA aircraft parked on the apron, but you can't go directly from a spanish airport to Gib. If you think you may need to divert from Gib (not uncommon given the interesting wind and weather conditions) make sure you carry enough fuel to land somewhere other than Spain.
You'd be wise to phone up Gib ATC and have a chat about the local rules before you commit yourself!