Noob question: would an illusion affect wearable armour?
 

Im a dwarf rogue, and I cant wear a treeweave, but I have a mask of obtenebration which would turn me into an erudite which can wear a treeweave. Would this work?

no

Race illusions do not affect the armor you can equip .. Get a piece of your class armor.

Warrior? Crafted armor or Indicolite.

Paladin? Deepwater or Valorium.

Cleric? Sol Ro quests (Ardent, Devout, Reliant, etc.) or Donal's.

Rogue? Ravenscale or Shadowbound.

Mithril Breastplate is good on a rogue for the slot you are asking about.