"seminarians and priests have been forced to lie about their sexuality"

No one is forced to lie. Lying is always evil and to lie about your same sex attraction when entering a seminary is gravely immoral. I would opine that it invalidates the would-be priest's vows in the same way that even concealing mental disorders can invalidate a marriage. 

Deep-seated same sex attraction (SSA) is a grave disorder. I precludes the possibility of entering a priesthood. Those with SSA have a cross to bear, they may be good people, but they are not in a state of health that the priesthood requires.