Should I assume from your question that your thought is that none of Putin's oligarch cronies happen to be in the arms business?
No, I assume you are resorting to the standard conspiracy theory said about all wars ever and that rarely makes any sense beyond the purely superficial
Why do you think oligarchs need a war to make money from the arms business?
Russia is autocratic. It can just increase spending to whatever level it likes, and a lot of the money they make comes from siphoning off money from these defence contracts. So the state overpays, and the contractor under-provides.
Wasting money actually fighting a war means there is less to be spread around the oligarchs.
Generals profit by having 'ghost soldiers' who they claim wages for but don't exist, by not running training ops they are budgeted for, etc.
They don't need a war, and in fact, wars show up a lot of the corruption that has enabled people to get rich when militaries underperform compared to expectation as their equipment is not up to scratch, and training is poor, etc.
And this is even without the threat of sanctions that make oligarchs much worse off and limits their freedom to enjoy their vast wealth.
So, what are the rational reasons Putin et al. are getting richer from this war than they would be without it?