I think the Emperor with all his legions would probably be able to win against Revan, simply because the army was, I think, more powerful.
There were several divisions that consisted of hordes of soldiers. However, if the Ordo Malleus and the other Ordo- groups were excluded, Revan could win - unless the Emperor had powers yet unknown; I mean, he's called "Immortal" and "God," so I would be suprised if he didn't have some massive badass powers on his side, largescale and smallscale. However, he was no match for Horus, so this seems false, unless Horus was a "God" too. So, I think Horus's legions might make Revan's forces into toast.