I've got news: sexual orientation has been used as a reason for denying security clearances up until now and probably will continue to be. I know people in the field who noted that on several occasions gays or those who engage in gay pursuits have been put in compromising positions based on their sexual orientation.
A person is only denied if they can be blackmailed.
What that means is if they lie about their sexual orientation, then they aren't given a clearance.
If they are open about it, then they can get a clearance.