The only thing that makes such a marriage a sham is one or both of the partners not being honest (with themselves and/or their spouse) about their sexual orientation. Mixed-orientation marriages (although fraught with challenges) can be successful, while giving children a stable and supportive home environment.

Regardless of the sexual orientation or gender identification of either of the partners in a marriage, the most essential factor is honesty and the conscientious maintenance of trust. Love is of ultimate importance, too, of course.