"Does that work with units or com only?"
Yes and no.
Every unit can turn on "snipe mode." But snipe mode acts differently for different units.
The behavior of a unit on "snipe mode" is different because it completely changes the target priorities. They will target certain things before other things, like they will target a nuke launcher before they target an SMD before they target a pgen before they target a tank. It's like they attack the most valuable targets first, instead of trying to fight with enemy units.
CERTAIN types of units (I will list them) are allowed to have ACU target priority, meaning that when they are on snipe mode they will shoot the ACU before they shoot anything else.
OTHER types of units are NOT allowed to have ACU target priority. If you put them on snipe mode, their behavior changes, but they WON'T prioritize the ACU above shooting other stuff. They will still target nuke launchers but they won't prioritize the ACU.
Units that will prioritize the ACU while snipe mode is turned on: Experimentals, ACUs, LABs, gunships, fighter/bombers, and maybe sniper bots.
You can also select "ACU" target priority from the target priorities mod menu. If you do that, units that are ALLOWED to prioritize the ACU will. But units that are not "allowed" to prioritize the ACU will not prioritize the ACU. This is different from snipe mode because I think it only affects whether or not the unit prioritizes the ACU. It doesn't make the unit prioritize a t3 pgen before an enemy tank.
One weird thing about this is that you can select LABs and turn on snipe mode BEFORE you put them into a transport, then when the transport is in flight, the LABs will target the enemy ACU. If you're going for a ghetto gunship snipe, you should probably turn on snipe mode before loading the transport...