I've seen it claimed that the world's richest man is not Elon Musk, or Jeff Bezos or Bill Gates, but rather Vladimir Putin, with secret assets & accounts everywhere.
It's also claimed that Russia benefits more by high energy prices than it loses by Western sanctions, and so their war is justified on economic grounds alone.
As for Ukraine, I've seen no reports suggesting Zelinski is as corrupt as Joe "the big guy" OBiden, much less corrupt on the scale of Vlad the Invader.
So you really can't use corruption as an argument against Ukraine.
As for American interests, what's in our vital national interest is that Russia's invasion of Ukraine fail, and thus discourage China from invading Taiwan and any other two-bit tin-horn dictator from invading their weaker neighbors.
If Russian aggression is stopped in Ukraine, the world will be a better place.
If aggression wins in Ukraine, we will see much more of it in many other places.
That would not be in our national interest.