Have you confirmed that with the IFComp folks? IntroComp's FAQ says otherwise. Near the bottom of http://introcomp.org/, one of the questions is "When I finish writing my game, can I submit it to IFComp?" and the answer is "Unfortunately, IF Comp's similar "no prior release" rule makes taking this route impossible. However, you still might be able to enter other competitions - check with each comp organizer as appropriate!"
Hi Josh! My plan is for people who want to go the IFComp route to hold off on releasing the game on itch.io and just send it to me or others privately for feedback. It might be possible to upload to itch.io during the week of the jam and make it private or unlisted to facilitate this private sharing -- I'll be able to confirm this Monday.
Ah, that makes sense. You can definitely make stuff private on itch: at the very bottom of the "new project" page, choose "Restricted" instead of "Draft" or "Public". You can choose to set a single password that you can give out, or (more flexibly) you can go back to the game's Edit page, choose the "Distribute" tab and generate one or more download keys which can be claimed by an individual person or revoked so you have more control.
I suspect they won't let people add restricted games to the jam, but as jam owner you should be able to come back and add it once they make it public: I'm nearly certain that you can make whatever exceptions you want to the rules about when people can submit games.
