Grant wasn't personally criminal, he was just a really poor judge of character in his hiring decisions.
I know, that's why it dodsn't work. His entire cabinet were criminals, though. Comparable to Trump. It wasn't intentional for Grant, like with Trump how it is by design. Like you say, Grant had a poor judge of character.
...he was also...not that great of a general. His "overwhelming force and kill until they surrender" isn't really a brilliant strategy, it was just desperate. I think most military historians look at McClellan's early war plan as solid and a winning plan, just not fast enough in Lincoln's mind, early in the war, even though in hidsight, it probably would have ended things earlier than what would have happened.
....now that I think about it, may have even helped with Southern bitterness through Reconstruction and saved Lincoln's life, if it could have, say, meant that Sherman wouldn't have to be Sherman, lol.