Strictly RAW, I'd say no:
Etheric Rounds (1 to 5; Renewable)
Produced in top-secret, experimental laboratories around the country, these bullets have been bombarded with a cocktail of exotic, high-energy particles that infuse peculiar pseudo-physical properties into the lead.
Emphasis mine ^^
However, I've found that most of the World of Darkness games provide rules that can be dressed up as you like.
Ask with your Storyteller if the same procedure could be applied to the inflammable fluid of a flamethrower.
I'd say It should't affect the balance of the game (since the supernaturals entities are a LOT more powerful anyway) :D