jarrod:
Er, you sure? I thought AM2/AM3's VF2 & Sega Rally engines were officially made part of the the Saturn SDK in 1996? I saw plenty of reports that these engines were later used in 3rd party games too (notably in Tecmo's DOA and Jaleco's Super GT 24h ports from Model 2)... was the entire mid 1990s gaming media mistaken?
The actual engines weren't included in either the Saturn or Model 2 developer toolset; the newer libraries for those systems were rewritten around the work that AM2 and other internal divisions had made with top games like Virtua Fighter 2 and others.
When designing the original Dead or Alive, Team Ninja's first such 3D fighting game, they sought some assistance from AM2 for the fundamental mechanics like getting the fighters to smoothly and responsively transition between different move animations and interactions. They didn't learn any specifics from them -- just that AM2's method was different than the direction they were headed. So, Team Ninja decided to continue their own way.
While Team Ninja benefited from the extra maturity of the Saturn's and Model 2's development environment evolved by SEGA's game studios, and also from the benchmark established by Virtua Fighter 2, they actually wrote their own tools for programming the games.