The vaseline wouldnt help a triangle or high guard very much considering it was rubbed in on the middle of this shoulder blades. Usually on this point of the back there is very little contact even in high guard. I know what high guard is and usually (depending on how the person locks their legs, there will be no contact at all in the area. I don't know any kind of triangle that goes inbetween the shoulder blades.
I tried to find a picture of high guard but I gave up, google failed me.. but anyway. Unless the fighter is close enough that the defenders leg is completely horizontal across the back and his other leg is locking his foot down like a triangle then that MIGHT make a difference but I doubt you would be able to tell(espescially with how sweaty the fighters are).