It depends on the fantasy, In Futuristic fantasy i could see it but not too much. In Medieval try not too. Instead of something like son of a b*tch you could do something like son of a swamp hag.nice - good lesson
I got an idea for my story but it might be a bit longer then the one page (I'll try not to make it too long but I don't it to feel rushed)
Also if the main characters were soldiers, and I'm writing a fantasy, would it be appropriate if once in a while they were to swear.
(You said it would be inappropriate if characters swore in fantasy, but it would be a normal attribute for someone of that occupation to have)
Fantasy = Be Creative