I have only dated Greek men. Unless I found someone spectacular, I would definately not date a non-Greek. This may be because at my school 85% of men are Greek and if they are not there tends to be a.... reason. Either they:
a) act really, really, really sketchy when drunk
b) sort of hole themselves up in their rooms all the time
c) are just not interested, which usually means they're not interested in the same things I am
Outside of my college or after college I would certainly be open to a non-Greek. But I think me and my current dude might just go the distance, anyway!