I don't want to speak for anyone else, but if it isn't allowed, submit a game anyway. It's incredible that there are so many young people in this jam (I guess we have Brackey's videos to thank for that, so a special shout-out to the man), but unless the jam calls for specific engines, which this one doesn't, if someone tries to discourage you from participating because you're using Scratch then they should be flung out a series of windows.
Making games is kind of like being a Wizard, or a little God, creating your own worlds and inviting people to enjoy them. No one should be discouraged from being the master of their own Universe. If you do get discouraged... do it anyways.