You can kill the occupants in the vehicle under the IFV-6C panther, strider, Ifrit and Hunter, CH-49, Marshall, GhostHawk, AH99, PO-30, Mi-48, Marid, T-100, and the M4A2 Slammer.
You can bend your screen up through the bottom of every vehicle. The only vehicle you can't look inside or shoot up inside from below is the quad. {F21099} {F21100}
I can confirm this ticket is valid. I tested in game and I found that there is no collision with the soldier's weapon when you climb under a applicable vehicle.
Artillery vehicles aren't affected, as the turrets are placed higher up and can't be reached through glitching from below. At least not from my testing with all closed ground vehicles.