I'm not really sure what the situation is with fan art. At one stage PT could not support it due to the amount of bandwidth it required to store a lot of pictures. I'm not sure whether that restriction was ever lifted, however.
In the Miscellaneous Guilds section, there is one called something like, Tolkien Artist Guild. You might be able to pick up a few pointers in that one. At one stage Plastic Squirrel was going to make space on his own site for those who wanted to post such pictures, but I'm not sure whether anything came of it.
Your best bet, if no one gives you a better answer in the next few days here, is to PM Taz with the same question.