Geomancer few questions

I recently pulled Geo and have some questions regarding his passive and build:

• does debuff spread of HP burn for example from Vizier works with his passive? Does it count then as applied by Geo or Vizier?

• is it worth building him with offensive tree and warmaster? Can warmaster proc with his passive?

I have 2-key UNM unkillable team right now with Gnut as my DPS, I’m trying to figure out where to use him the best. I tired him in Hydra, but I also see TTA defense teams using Geomancer.