I'm sure that on a personal level,Tom felt bad about Fredo's killing. He also knew that there was no way he could broach the subject with Mike.The smart move was to sit back,offer no opinion either way,and let the chips fall where they may. Mike was never going to seek Tom's advice and despite his other shortcomings (i.e. not Sicilian,not a wartime consigliere) Hagen had a great instinct for self preservation.