Every single gun company says don't use reloads. It's not a "chamber support" issue, it's a CYA issue. Glocks will work perfectly with any ammunition that generates a peak pressure spike of 35,000 PSI or less, in accordance with SAAMI specifications for .40 S&W ammunition. Ammo which exceeds this, accidentally or intentionally, will very likely result in a case failure, and hot powder gas venting into the mag well, and probably crack the frame. IIRC, about 40,000 PSI is enough to cause a catastrophic failure. Many guns have a failure point around the same pressure. There was a police department on the west coast a few years back that had something like 3 H&K P7s self-destruct in as many weeks.
Buffalo Bore's warning may just be a CYA, or it may be a tacit admission that their .40 ammo, like their "Ruger only" .45 LC ammo, exceeds the industry standard safe pressure limits established by SAAMI.
Either way, I wouldn't risk it. If you really want to shoot the stuff in your Glock, either get the feed ramp TIG welded, or buy an aftermarket barrel with full chamber support.