I would say that the exhaust gasket is necessary. If not, hot oil/fuel will leak out around the connection ruining your pants or burning your leg if wearing shorts.
I just bought a roll of gasket material from tractor supply for $4 and used gasket sealant with it. They were out of the thicker gasket material so I just made two and stuck them together. So far no leaks. I think the high temp rtv might have been easier though. At least I have plenty of material for gaskets now.