"Fredo and his men" is one of those script anomalies that pop up so often in the Trilogy. In NY, Vito and then Michael had real Mafia regimes with capos over them to conduct illegal business and provide muscle. In Nevada, though, Michael's businesses were legitimate and, as far as we see in II, security was under Rocco, probably hired guys not made men or associates. If Fredo had men under him (a regime), what would he need them for? The chart shown at the Senate hearing listed "Caporegimes" but it was historical and included Tessio and Clemenza, as well as Sonny.

Fredo was a minor figure in GF and in the novel. He was somewhat weak and ineffectual in the novel, but the movies portrayed him as an idiot. Ironically, that treatment made his betrayal of Michael, and the boathouse scene, all the more powerful and shocking.