His jam session is not completely useless, it's actually an easy poke tool. I mainly use it to stop people comboing or disrupting an level 1 super. In 2v2 it can really help your teammate if someone is setting up a super.
What I noticed with the bread and butter combo, is that sack needs to be really close to a opponent to link the Up Square grapple. I don't know if it always works, but mostly I try to walk forward a bit to connect the link.
As for the bnb combo, I tested it out and it simply does not work on characters like Toro and Jak.