that is there choice. personally I would not because makeing a cover takes time. even simple edits can take an hour. drawn can take five. imagine spending that time and then person dont use it. I would feel used. and the cover properly could not be used for something els.
its people own choice to make this contest and entering them. I just dont like it because its kinda like you are asking people to spend time on something you might not even use. that is why I find it better just to ask someone to make a cover.