I may not like a good amount of his comedy...but hell, I want his big band album.
Or some good PR advisors.
If you listen to MacFarlane talk about one of his seemingly nerdy interests (Westerns, science education, big band music and show tunes), there's CLEARLY passion there. Heck, Million Ways To Die in The West was a mess, but it clearly shows that MacFarlane LOVES westerns.
The movie also showed a clear geekery about various aspects of history, which I find incredibly endearing.
Sadly, I don't think those two things (geeky interests and sexism) are incongruous in the slightest. I don't know enough about McFarlane to affirmatively say "he is a geek!" and "he is deeply sexist!" (from what I know about him I think the first is likely to be true and don't know enough to say one way or the other about the second). But I think "someone is both nerdy and at least to some degree sexist" is a more common/simpler explanation than "giving money to geeky causes is a way to deflect attention from a sexist action."
Again, there's a huge difference between being nerdy and making splashy gifts to causes (and a one million dollar *matching* gift is surely splashy). Also, I can't see how someone could watch those Oscars and not think that he's sexist, but that's just my personal view.