Are the blocks that are mined on jtoomin's fork empty, like they were on the main p2pool?
No.
I think when I was on, a few people were testing jtoomin's fork, but I thought that it was supposed to get merged with the main p2pool. Is that not the case anymore?
Mainnet P2Pool must support altcoins, and jtoomimnet currently does not work properly with altcoins. The merging of jtoomimnet into mainnet is therefore
on hold until jtoomimnet is made compatible with altcoins.