Well, I believe so but you would run in to problems when trying to submit the Game on Itch.io, you would need to put a url with the Scratch Game in the Description. But you are free to use whatever you want. Quote from jam rules: "Apart from that you are allowed to use any game engine or framework" And Scratch is a sort of Game Engine
You can't link a project in a describiton or you will get disqualified. On github is a program that will convert scratch files to HTLM5 files which can be uploaded.
You have to use a 3rd party tool to get a file to upload to itch.io. The other person said to put a link, but in the jam rules it clearly states that it is not allowed and will get you disqualified. You cannot use scratch unless you use 3rd party tools, so I would recommend figuring out how to do that.
