Thinking about that. I think that's how I do read the book, but what would change if Nick felt he'd been manipulated? He already knew Gatsby had done things for his dream that hurt others, directly or indirectly. And getting a job and house he otherwise might not have isn't terribly harmful anyway, unless one counts the disillusionment he came to suffer, which a) Gatsby couldn't have predicted, and b) might end up being good for Nick since it sends him home?

I find it superfluous because Nick does know Gatsby's using him, even trying to bribe him, and helps anyway. Maybe he'd have reached some human limit and not helped him if he'd thought Gatsby had researched Daisy's whole extended family etc., but is that important? Nick decides that, at least in comparison to Daisy & Co., Gatsby is the good one, since his monstrous actions are dedicated to something and not half-assed assuagements of vanity like those of the Old Rich are. Would learning he'd been a pawn to start with, that Gatsby's smiles of reassurance had been calculated all along, have changed things?