Hand drawn is perfectly fine! It will just ultimately need to be scanned to be submitted. The computer specifications would then just simply apply to the scanned copy. Let us know if there is a problem or question with any specific requirement.
Traditionally, mascots that are computer drawn, or at least look like they are computer-drawn, win in contests for the mascot at any con--however this is not a requirement!
You might consider applying computer techniques to the scan of your hand-drawn art, after scanning.