I've seen other people post them. You may want to post them under a separate account, though. Not because Tapas might ban you, but because you're only allowed to have ad rev/ tipping on original content, and you can only turn it on/off for your entire account instead of each comic. So you could have one account where you post fan work (no ad rev/tipping) and another account where you post original content (with ad rev/tipping).