I would argue that they are better than unhappy assholes.

As a corollary, the happier the assholes are, the better person/more agreeable they would be, and I have found that statement to be true.

That doesn't say anything about whether making them happy in other ways reduces their assholishness. It might do. (Perhaps they have a certain happiness setpoint, and if they're not made happy enough by other things then they'll achieve it by being assholes.) Or it might not. (Perhaps they associate happiness with assholishness, and an increase in either provokes an increase in the other.)

Ok, what if being an asshole makes one happy? ;)

This sounds highly implausible from what I know of happiness. Being an asshole helps them cope? Sure. Makes them happy? No.