It is allowed as long as it isn't excessive to avoid triggering any players. The jam's goal is to be open for all which is why the rules request to avoid any exaggerated violence. If you find it necessary for your game, keep it as light as possible. And if you are unsure whether or not you can limit exposure to such visuals in the context of your entry, the best thing to to is to scrap the idea completely or simply find other less triggering ways to get the idea accross.