Hi Henry,
Depends... not the underwear, the other depends. I haven't seen the videos on the belt's sites, but I have 2 StealthBelts that Warrior gave me, which I use as patterns for my own BobBelts. The non-neoprene Stealthbelt is a relatively thin Spandex, and you don't wear it so tight that it strangles your stoma. You just wear it tight enough not to fall down. When worn that way, it's not very restrictive to your stoma, assuming your stoma doesn't stick out very far. The Neoprene version is similar, but you'd probably wear it a little tighter if you're wearing it for protection when surfing or MMA fighting. If that one is worn too tight, I could see having the problems you're describing. When I make mine, I'm going to make the outer layer of the belt looser than the inner layer where the pouch for the bag is, so the bag has room to expand and the outer layer won't press on my stoma, like you're describing. I should also note that my StealthBelts are a few years old now, so they may have changed the design to address your concern. If you're contemplating laying down that kind of cash for one, I'd send them your questions and let them explain what they're offering. If you want to try one of the ones I've got (never been worn except to check the waist size), just let me know and I'll shoot it out to you. I'm not sure what size they are... I wear a size 35 waist Levis and the Neoprene one is tight; the Spandex is simply too small for me. But you can always add a bit of Velcro extension to make it bigger, and there's about 6" of adjustment in it to make it even smaller.
Regards,
Bob