The VX (and VT) V6's run ALDL I know it has a OBDII shaped plug but if you plug an OBD2 scanner into one you will get nothing. The V8s (5.7L Ls1/GenIII) run OBD 2.
However as with all LS1/GENIII engine control units the OBDII fault code retrieval is non-standard so you can't use a generic hand held scanner (like jaycar's) UNLESS it has been especially modified for the GENIII.
Later on the Alloytech (VZ's) and the 6.0L LS2/GENIV run OBD but a different type (CAN) to the LS1 (VPW).
So in summary.
VR->VY V6's run "ALDL"
VR->VT S1 V8's run "ALDL"
VTs2->VY 5.7V8's(not 100% sure when the 6.0L came out) run "VPW OBDII"
VZ->VE V6 run "OBDII CAN"
VZ( or when ever they changed the V8 over) -> VE 6.0L V8 run "OBDII CAN"