This is all theorycrafting but at least with my understanding, nothing'd stop you from using custom sounds for anything, assuming you get the game_sounds_something.txt files to properly and reliably load to do what you want.
Sv_pure no matter how many times it says whitelist is at the end of the day actually a blacklist that only fully blacklists a few folders, so a sound would still "work" in sv_pure if it's inside a folder like scripts or resource or literally anything that's not sound, models, materials, or particles. The only issue is that if it's there, it's not replacing anything, so you'd need game_sounds to reliably work to replace things (where you can just add ../ in the specified file location to bring it outside of the sound folder and use a sound from literally anywhere).
I experimented with doing basically the same thing with materials before vmts stopped preloading (despite there already being replay/thumbnails/, I wanted to see if I could, and I could). My experience with game_sounds is really hit-or-miss and I personally don't want to mess with it much, but if someone figures that out then you should be able to do whatever, unless I'm missing something key.
Probably going to be patched at one point or another but eh.