Yep. Prevailing military opinion against using poison gases could have changed over the course of the war, of course, but he brought both the technical knowhow and the outspoken advocacy. The Allies' first alleged use of poison gas turned out to be an unfounded rumour which Haber himself was responsible for disproving.

Didn't take the Allies long to muster a response though, and they had their own Nobel Laureate Victor Grignard to build chemical weapons for them.