I've run mine quite a bit at high temps, 400° - 600°. So far, I have not managed to catch it on fire, yet. If you are feeding pellets with a lot of sawdust on them, I can see how that might accumulate on the ramp and flash over, but it'd be a pretty short lived fire I'm sure.
The grill is made out of 201 stainless. More info on 201 SS
here. Short story is that 201 is essentially the same as 304, but it's cheaper. For our application, it performs the same.
Your second paragraph on the design is exactly on point. The indirect side is SO GOOD. It's really simple and genius all at the same time. Results are just killer. Easily have turned out the best ribs ever on this thing. The other thing is that it is able to get serious smoke flavor, even at higher cook temps. When I used to cook at 275° on my GMGs, if I didn't pre-smoke for an hour (at least) I just wouldn't get any smoke flavor. With this thing, I cook straight through at 275° with no pre-smoke period and I get great smoke flavor, in about half the time since I don't have to cook at 180° for extended periods to get smoke on the meat.
These STL ribs...mmmm....just look at 'em!