Roemer starts his book on Accardo with the jewelry heist story, including all the gruesome murders done on behalf of Joe Batters. He didn't paint Accardo as a saint, not at all. It was the first substantial book I read about Accordo en I never got the impression that he was a nice guy or even not a ruthless murderer. I half remember him also writing that Accardo had made a plan to have his legs broken or something like that, after he retired from the FBI.
It's just that the contrast with guys like Alderisio, Fifi Bucieri, Mad Sam and Giancani was rather big. He certainly disliked swaggering mobsters as those guys were, and especially with Giancana it seemed to be a personal/ego thing.
The guys I remember as being the 'nice' guys from his books are guys like Gussie Alex and Murray Humphreys. I don't remember them being associated with too much violence in the years he writes about, but it's been a while ago since I read his books.