Here I'll attempt to list all mods that work together with KVR as well as ones that don't, if you have any suggestions or are a mod maker yourself, don't hesitate to comment. This doesn't speak to compatibility between the mods themselves.

Known compatible:
Vanilla Firearms Expansion
Gunrunner's Weapon Pack
Realistic Advanced Trajectory

Very likely compatible:
Kitsune's Crossbow Mod and all its variants and tweaks.
Blackbeard's M&P
Blackbeard's Operator M4
Blackbeard's AR-15

Contains modded ammo types unsupported by KVR (might be added in the future):
VFE Stalker pack

Conflicting:
Firearms B41
Brita's Weapon Pack / Gunfighter mod
Snake's Ammo Maker