Bioware's "Knights of the Old Republic" RPG used what was basically the d20 system, as did its sequel. So there's certainly ample precedent for a video game to use the d20/OGL/whatever system as its core mechanic.
I always presumed KOTOR and sequel used the D20 system as they were licenced from the D20 SW RPG from WOTC and Lucasfilm. Using this system also allowed Bioware to use the NWN Aurora engine which they already had - which was developed to run a licenced version of D20 D&D following the move to 3e (BG2 being based on 2e AD&D).Bioware's "Knights of the Old Republic" RPG used what was basically the d20 system, as did its sequel. So there's certainly ample precedent for a video game to use the d20/OGL/whatever system as its core mechanic.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.