Shaba didn't write their own code. They were simply handed the same SDK Neversoft used for THAW.
As soon as THAW was out the door, or probably before then, they stopped editing their SDK. That's why levels are cross compatible with THAW and THP8.
Since this year I won't be as busy during school time, I may release some hacked up ISOs of some fun shit I can think of.
Gawd, I hope THPG for PS2 will have netcode, but it won't