It was actually the real Emperor, that we can say for sure. And he was struggling in that battle, he almost died. And he never used his lightsaber, just Revan's. And the Sith Emperor doesn't have a sense of humour.
they probably faced just a Voice and he wiped them like a dirt off his robes - he even tried to be funny and use lightsaber ( which failed but this is rather a weapon for simpleton comparing to Emperor's power ). Immensive knowledge of sorcery and alchemy would allow him to drink Nihilus like a good dark cherry juice.
And he ain't going to be drinking Nihilus. He's a black hole AKA nothingness. You get sucked in, you not consume it. Nothing to drink I'm afraid.
EDIT: Lol are you always high?