In OP's context, not to say means and possibly even or if not (i.e. - not definitely, but maybe).
In effect, whilst the writer is definitely prepared to say there is deep ambivalence (felt by observers), he's diffident about going so far as to say there's hypocrisy (being observed).
One could say this is a mild form of paralipsis, typified by "not to mention xxxx". In that more overt form, the speaker claims he won't mention xxxx in the very act of so doing (but he definitely and explicitly means "xxxx really does apply here"). In OP's case, the writer shies away from explicit accusations of hypocrisy, he simply raises the possibility in the reader's mind.
I'd also say that to me the sentence is poor English. The "ambivalence" is an attribute experienced internally by the writer and/or other observers, but the hypocrisy (if indeed there is any) would be an externally assigned attribute of whatever/whoever is under consideration. I think it's bad style, if not downright unsettling, to conjoin attributes with totally different referents in this way.