Maybe it's possible to orgasm, but it hasn't happened for me. Has grinding been exciting for me? Sure... But I require being penetrated to really get a fully satisfactory experience. I would imagine that gay men who don't like anal intercourse (and they do exist) can orgasm based on frot. EDIT: OH WOW, I'm super stupid at this hour. Grinding is sex, hun. I mean, otherwise the frot people are "non-sexual", and I'm not sure they would think that's fair to them.
I havent ever done penis to penis grinding but i like to tease boys by grinding on them while i still have my clothes on, its fun and its better than me being naked lol.
I dunno about guys, but I know it is very possible with women to orgasm from grinding.. I guess it is just a matter of what turns you on or not.