Are “Destroy” Powers “Damage dealing” Powers when used against Durable Invaders (e.g., for Flame's Fury)?

Are “Destroy” Powers “Damage dealing” Powers when used against Durable Invaders (e.g., for Flame's Fury)?

Yes.
For example, Asphyxiating Smoke deals 2 Damage to 1 Durable Town, so that can be increased to 3 Damage to 1 Durable Town by Flame’s Fury.