Yes, having structure and a deadline helps move things forward :D
Progress on ongoing stuff definitely counts. There's no finite set of rules and obligations in this jam because I host these jams and currently they are unranked so no one feels like it's a competition or too much pressure with life complications
I'll run long and short jams so depending on people's schedules and procrastination, they feel they have a doable jam. I like short jams for myself because I feel it's best to get many small works out for employers to see.
I see many jammers, developers, artists, and more say shorter jams with more work = more hiring. Of course, this is what I'm noticing and my opinion.