I have never had one, knock on wood, but from assorted posts on this site it seems like hopper fires don't really produce a large fire (with flames) that would catch near by combustibles on fire. I have read where the coal at the bottom of the coal hopper may be glowing but the main product of these "fires" is fumes and CO. Still, nothing to mess around with, but I don't think flames shoot out of the hopper relentlessly.
On my koker, the glowing part of the coal bed never moves upstream of the grate vents, but the blue flames will migrate (waft) towards the back, most likely just being blown around by the combustion air. The air is blowing through a good 2 inches of coal, so some of it will wander a little and not blow straight up.