I'm in a heroic raiding guild with four female raiders, myself included. I also raid lead and organise our strategy's with my boyfriend.
My very first hardcore raiding guild back in TBC was lead by two girls, hell the main tank was also female as well as a few other members. They're top 300 world rank now, though I don't know who from the old crew still raid with them.
I have never seen any guilds with gender restrictions. I'm from the EU though, maybe things are different on the US?
What do you mean by hardcore, 8/8 with 30% nerf or killing morchok on heroic.