Right. AFAIK, you stick a cart into the top of the rumble cart, and it gives it rumble privileges (or however you'd like to call it.)
And Pocket Monster Go! Go! 2 is published by 'NEW GB COLOR". These guys published Zook Z and a couple other games for Vast Fame. This, may as well, be a hack of V.Fames.
I do remember hearing of a KOF hack by them, so this'd be a hack from before 1999. 1999 is when they started developing pirates.
Hope this all helps, man.