The 3 guys who turned informant on the activities of the Demeo crew

Freddie Dinome
Vito Arena
Dominick Montiglio

None of them mentioned Kuklinski even in a small form.
Vito Arena may not have known about him but surley Dom and Freddie would have heard of Demeo's "ice-cold killing polack".

As I said earlier, I believe he bought merchandise (firearms, porn etc)off Demeo and nothing more.