It sounds weird. The issue here is that bliver denotes an action, while være is for conditions, so "Var han behandlet?" sounds like "Was he a treated man?"
A nicer example might be the following:
- Var lyset slukket? - Was the light switched off? You're caring about the condition of the light.
- Blev lyset slukket? - Was the light being switched off? You're caring about someone having actively switched off the light.