not that i'm in any way up to date with how most OBD2 things function, but from what i'm TOLD........

GM liked to blend the speed-density and MAF calculations in at least a few applications, others seem to be done almost exclusively in MAF, with speed-density being used for transient conditions, but rarely have i seen speed-density being the primary airflow calculation(except for the applications that obviously didn't use a MAF).

but i really have no way of knowing for certain. easiest way i could think of would be to use a roadrunner, sit at idle and change the MAF value that corresponds to the airflow you see at idle, see if it effects fuel trims, then do the same at cruise speed. then do the same process with the VE table.