You mean the one on the end of muffler? Yes, but remember, that's only a lock nut. If you don't have the main bolt through the whole muffler nice and snug, the whole rear can (and the baffle inside, if it's still there) will slowly loosen off.
I tend to nip everything up, and then lock down the lock nut.
As for muffle gaskets between the engine and the muffler, I don't. They always seem to compress after a bit of running, leaving the bolts loose.