Depends on the circumstances...
If in a PBEM game both you and your opponent agreed it's okay, by all means.
If you're playing solo and you believe it's okay, go ahead.
Just remember that if those drivers were under Joe Stalin's order No. 227 "Ni shagu nazad!" probably they'll even attack the enemy, not just observing
Kinda reminds me how the Soviets stormed a village, and then each villager, old men and children included, were compelled to follow behind the tanks for assaulting another village, despite only 1 in 10 were given rifle.