My understanding is that the VASIS will give you a 3 deg (or whatever it is published as for the particular serodrome) glidepath regardless of whether you fly one dot high or low. All that alters with the VASIS is the actual height above the threshold that you will cross at. ie if flying one dot low in a particular type it will correspond with a touchdown pt of 500 ft in but still on a 3 deg glidepath.
On the otherhand with a PAPI the change in lights provide you with the feedback of the different angle of approach. In all cases with the PAPI however your impact/touchdown point remains the same.