It's kinda hard to wrap your brain around sometimes, but bad people can be patriots too. When you have a proper, full-scale war going on, these people become a resource like any other.

Anti-corruption is great during peace time. Necessary, even. But it cannot always be the top priority in all situations, that's just not practical.

I would even argue that if you're not continually adjusting your priorities as situations develop, you're not a very good leader. So yeah, buy his guns now. Throw him in prison later. Can even confiscate back some of the money you paid. You have to win first though.

Expecting ideological consistency from a small country fighting for it's very existence against a much larger country is always going to lead to disappointment.