Seeing as they showed up anyway in RL, I think it's to be expected that they'd show interest in showing up. I think accepting their aid will merely strengthen the Anti-European and Anti-EverythingNotChinese sentiment of the Chinese people. Unless you feel like you really can't put the rebellion down on your own, I'd kindly decline Russia's magnanimous offer to become involved in Chinese affairs, before everyone else jumps onto the wagon :) Or at least set some conditions on what they can and can't do on Chinese soil.