I haven't, but that sounds really cool.
As long as the shared audio resources are Jack and ALSA, and SunVox doesn't require exclusive access, it sure seems to me like it should work.
The audio host duties of pi-Stomp are all handled by MOD. I don't see any mentions of SunVox on the MOD forum (
https://forum.mod.audio/), but theoretically, if someone has got MOD and SunVox to play nicely with each other on the same system, then pi-Stomp should too.
If you get it to work, please report back!