Is Battle Armor (or infantry, I suppose) swarming or mounted on a mech affected by fire on the ground in the hex?
All Other Units: Unless the controlling player gets an 8 or higher on a 2D6 roll, any unit that ends its Movement Phase on the ground in a burning hex or moves along the ground into a burning hex is destroyed.
Technically, the swarming/mounted units are "on the mech", not "on the ground", but you could also argue that they are close enough to the ground that they would be affected by the fire.