First off, if there were no details left out of the story and things actually happened the way they were presented, the HK rep should have gotten the story straight and not twisted the OP's words around.
Second of all, I don't really see what the OP is so upset about. The gun was designed and tested to be used with certain suppressors. Why should HK warranty something that was clearly used outside of it's design limits?
The failure isn't HK's fault at all. That's the reason they have a list of approved suppressors to be used with that pistol. That way it avoids these kind of problems.
As far as HK evaluating other suppressors for use with their guns, it's not a bad idea. However, my guess as to why those two models were selected was probably they were the ones in use by the majority of LE or Military at the time.
I'll give you a analogy. Lets say I purchase a saws all. I know it's a saw and will cut things. I have a idea of what kind of work it's intended for. Lets then say I use it full time to cut down trees and to cut through 3" steel bar stock.
My guess is it was never designed for this kind of use. If I used it in these applications and it failed, it would be pretty darn ignorant of me to blame the OEM and expect them to ship it back to them and repair it all on their dime.
I've never had a problem with HK customer service in recent years. There was a time they were less than stellar but they have greatly improved. I'm sorry you feel you had a bad experience but I would say you caused your own problem.
If you were aware that HK didn't recommend the suppressor you were using, that's your own fault. You took a risk and got burned.
When we do hit it we hit it out of the park and send it over to China as quickly as possible to cheapen it and sell it.