I think that even if Tom was not happy with the way Michael was handling things or the way that Michael treated him, he could never bring himself to betray Michael. In a man like Tom hagen's mind, to betray Michael would have been disloyalty to the memory of Vito. It would have been like he was actually betraying Vito.
I'm just trying to be a bit provocative with this thread, and I recognize it is a long shot, but if we think of Tom as more than a two dimensional figure, there is the possiblity that he was out to undermine Michael ---- maybe even subconsciously.
After all if those stories about all the comedy he was playing with Sonny's WIDOW are true, that would be a betrayal to Vito wouldn't it?
