If Russia is really so strapped for military formations that can immediately attack Ukraine, it will be only because the other 600.000 regular soldiers in Russia cannot be deployed fast enough from the other parts of Russia. While the Belarusian army is terrible based on everything we know about it, it's also already close to Western Ukraine with its supply infrastructure close enough. There's also the possibilities that Lukashenko decided on carrying out independent actions on his own (the most likely case imo; this is the exact thing he would do) or that Belarus' intervention isn't simply an attempt to draw Ukrainians to the west while Russia continues in the south.
That is to say, if Belarus even acts independently in the first place. I hope they won't, as a lot of Belarusians will die if it does, and between them, Hohols, and Russians, I'd take them any day. Hopefully it would hasten the end of Lukashenko's little fiefdom though.