They've certainly demonstrated that they're rabid enough. The question would be whether they could orchestrate something that wouldn't erode the support they have - it seems that violence in Mecca or as part of the hajj would be all too likely to backfire on them. By definition anything like that would have to be against Muslims, though they might get some support if it appeared to be directed squarely against the House of Saud rather than just random violence.
But who knows - they've demonstrated that they have few if any qualms about violence.