This is actually a good idea.
However, I suggest that the "on foot" crew member should be visible as troops, and if the crew member is killed while out of the GV, then the GV should be considered destroyed. Otherwise, people would always exit the vehicle whenever it was stationary, would use their "on foot" crew member as a type of reconnaisance drone, and we would end up with the screening effect of terrain mostly nullified.
MH