I wouldn't say it's required, but certainly a lot of discussion will be happening there that won't be here. Additionally, you don't need to talk with people on the Discord, you can just lurk and observe. To be fair, all the info you need for the jam is present here on itch.io, and I don't think I plan on making any substantial updates to the jam for the rest of the month.

So, in short, not required, but suggested.