I've seen both of these things done in previous Strawberry Jams, so it should be perfectly fine. There's a section for "early work" when you submit your game to the jam, so just include some information about the assets you've used. Also, for a commercial game, I suggest not locking any content behind a paywall in the jam release. Instead, add a monetized expansion after the games are rated or have the paid version be very clearly separated from the free demo. There's not any sort of rule regarding this that I know of, but it will make the rating process go smoother, since your game will be fully available for that purpose.