I believe that Geary figured out that he was set up by the Corleones with the prostitutes death. But in true scavenger style Geary wasn't going to bite one of the hands that fed him. He had his Senator's office to hide behind and being a veteran of politics he was probably very good at dodging trouble. As long as he kept the prostitute incident quiet he had to believe the Corleones would too. A symboitic relationship. Most likely Geary had several lucrative symbiotic relationships besides Corleone and Roth. One fault he had, or mistake he made, was underestimating the power and determination of the Corleone's, but he quickly fell in line to feed like all good scavengers do.