I just watched the recent JaggedAppliance cast. Nexus lost his ACU to Blackhearts fobos spam when some of his Fobos ran into Nexus' ACU and stopped him. If the Fobos had friendly fire - which it should because it's artillery and it seems like most artillery does - then some of the shots which hit Nexus' acu would have killed the fobos that blocked his path and allowed him to escape.
It makes sense that if you use T3 artillery to shell an enemy position while you send in your tanks, suffering friendly fire from such a bombardment is a matter of due course. So... all the mobile t1 arty should do friendly fire.