I would do it if I knew in advance he was gay and it was just for fun. I could get into the experimental aspect without being hurt personally if he didn't just fall in love with my twat- I wouldn't expect that.
I think perhaps a lot would depend on how the girl felt about casual sex to begin with. A lot of women aren't too hip on "friends with benefits", preferring relationships.
HugeBrazilian, if you are interested in shagging a woman, please just be honest with her about what you want. Pretending to like her for more than an experiment could hurt her feelings if it doesn't go that way. No desire is wrong as long as the people involved know what they are getting in to. Good luck, and let us know if you find the right girl, and what it's like for you.
edit- like all aspects of sex, there is no one answer for "Do gay guys still get turned on by women?" It depends on WHAT gay guy, everyone is different.