Not only would heating the blade of a weapon enough for it to have any effect likely ruin the blade, the heat wouldn’t have that much of an added benefit when compared to the damage done by slicing the tissue.
A rag tied to the end of a stick, soaked in fuel, set ablaze and used poke at enemies in an attempt to transfer the burning liquid on to them, would (in my opinion) be a much more effective way of doing damage with heat.