I have to say under most circumstances, no they can't.
But, there is at least one in my life. I'm pretty much best friends with a girl, she's 5-6 years older than me, and we're more like brother & sister. Talk all the time, go out together to bars & scope out dates, etc. etc.
and its funny, because we've both been over this conversation before. Neither of us are into the other, but we both admit that there's a certain amount of jealousy from the other when she's with a guy, or I'm with a girl.
So, I guess if you weren't really open and clear with this other person, it wouldn't work? I'm 'friends' with other girls... but yes, there's always sexual tension involved between both parties. And it's lots of fun