Situ was the one that started calling the plane the Virut plane. He has been Emperor for thousands of years, so the name stuck. If he wasn't so untalented because of his race's lacking intelligence, then the first Sage wouldn't have replaced him. His six arms didn't give him any advantage over the Sage when it came to fighting with weapons.
The first Sage could have replaced the name if he wanted, but he knew what the plane thought about it, so he didn't bother. If he had gone ahead with it, then the plane would have reduced its support for him.
So while the battle sage monkeys totally hate Vipers, the will of the plane misses them. If not that these Vipers are from another plane, then the will of the plane will just snort and ignore their conflict. But it is the Virut plane against the Tarat plane, and there are big things at stake here, so the plane will support him with its best.