[pm90]

I don't think galdolf could predict the exact role Gollum would play. It was just a hunch on his part (or at least the book makes it look like it is)

[saraid216]

Gandalf's hunch was more of a faith-in-all-people kind of thing, IMO. That it turned out he was right twice (Gollum guided them into Mordor and was instrumental in destroying the Ring) really doesn't count that much in my opinion.