I have to take issue with "one cannot be a Republican and gay."
Now, I don't have much use for "Gay Republicans" who support the RNC's current party platform, because to use your logic one could not be a "Moderate and a Republican," or a "Progressive and a Republican," or for that matter an "American and a Republican" under it's current right-wing leadership.
Republican use to mean "fiscal conservative, balanced budgets, and a restrained foreign policy." Even as a Democrat I can support some of those concepts.

Especially since those concepts are so completely foreign for what passes as a Republican today.
As for Mary Cheney? It's not her fault that her father Dick only supports her in word instead of action. Of course, at the same time, I don't think that it could hurt her in the eyes of the GLBT community if she stood up to that type of treatment. She hasn't, and now we've got this thread.
Maybe....her becoming pregnant will let the show other aspects of the effects of Republican "leadership" regarding Gay Families, and they'll see their own hypocrisy.
I doubt it, but there's always some glimmer of hope.