Don't missunderstand me here: I am a very fond of the AI in RUS, however as you might imagine, there is a "but".
The Ukrainian could use some sort of AI. If I am not mistaken he has currently none.
As it is, you can take Ukrainian cities without any reaction. Kick his troops out of Kiev or any other city, the survivors retreat and sit in the next region for the rest of the game.
I know that it might be a bigger change to implement another AI into the game. But I think, attacking the Ukrainian as Southern White or Red should trigger some sort of reaction. An alternative would be to create some new events: e.g. perhaps if the Red attacks the Ukrainian first the Whites gets an option to ally himself with the Ukrainian and vice-versa. Not exactly historically accurate but still better than the Ukrainian as impassive punching bag.
It might be something to consider for patch 1.02?