I think it would be fine with a muzzle brake, it does say on there that they leave enough material to thread 5/8x24, so you could get around this by having it threaded 9/16x24 or 1/2x28 depending on the caliber you were using, and you would have a partial metal shoulder to help support, not just the cf. Or, HCA may be saying that there is enough material that a 5/8x24 thread would have a partial shoulder, so all the pressure wouldn't be just on the cf. I do not know.
I do absolutely see the problem with a direct thread suppressor though, it says in there not to exceed 240 degrees with cerakote curing, a supressor fired rapidly could easily exceed this. I would think you would want an adapter for sure, if you ever planned on any type of rapid fireing, it may even be an issue on a prs rifle, not sure how hot the can would get in a course of fire.