If we can assume that Locke found Ben's secret closet (since the door was wide open when he found Sayid) then it is safe to bet that he knows Ben has quite a bit of money.

When Kate told him that Miles asked Ben for 3.2 million dollars, Locke's reaction was ambiguous. Additionally, he never questioned if Kate was telling the truth, so I think he believes what she is telling him.

I am a believer in the "3.2 = code" theory. I'm just wondering if Locke is suspicious about this conversation in the same way many of us are, or if he just suspects Miles to be in all of this for the money.

I would think it would make him suspicious. Maybe we'll see a scene of Locke in the hidden room, going through Ben's things and then talking to Ben about them. Or I should say trying to talk to him. I doubt Ben will give him much information.

Maybe if Locke explores that room he'll start to re-think his "protecting the island" claim. We could see him lose faith again. Seems to be a trend with him.