(Tim) Hi! Glad you could stop by.
I'd say a jam is what you make out of it. As far as I know, most of the creators are active members of the Devtalk Discord, which is the biggest English visual novel development community on the Internet. However, the work itself is definitely quite solitary, unless your team does a lot of back and forth.
People in the jam can see other submissions as they roll in, and also play them if they so wish. I personally did go through the entries in the jams our studio participated in :) It's fun seeing what other people came up with!