haven't ridden the jam, but I have been riding an Undisputed for 3 seasons (the Undisputed is basically a stiffer version of the Omni).
Based on the specs:
the Omni has significant insert setback as well as a directional (setback)/more intense, powder specific version of TBT. Despite how powder specialized the tech, it's actually a surprisingly good all mnt board (except park).
the jam has the exact same stiffness as the omni, but has no insert setback (twin-ish) and only a relatively mild directional setback on the TBT. It's basically an all mtn board that you can take in the park, but won't perform as well as the omni in pow.