Personally only have 1 deity culture victory and, alas, I did build a wonder. However, I don't think it's necessary; I'm all but certain it wouldn't be necessary to build a wonder with any of the three civs that have culture UI's that amass tourism points through hotels/airports (Brazil, France, Polynesia) and probably not so with the rest.
I think a better question would be whether or not it's possible to win a deity level culture victory without any warmongering. There's always one civ that gets about a half dozen wonders pre-Renaissance and continues to horde after that. The culture they amass becomes seemingly insurmountable, and can only become influential if you take their capital, both removing hundreds or thousands of CPT from their production and adding dozens or hundreds to your own tourism.
As far as the one wonder to really shoot for, I agree that Pisa is incredibly valuable, but my vote is that it's second in importance to Sistine. Not that the theming bonus is that incredible, but rather so that someone else doesn't have that global 25% culture bonus that your tourism has to overtake. If one of the AIs that wasn't really focused on culture happened to build Sistine than it wouldn't be that big of a problem, but Sistine always seems to be a Murphy's Law scenario: whichever civ already has the runaway culture accumulation will always seem to get Sistine as well.
Of course, that's not to say that building Sistine is vital, but acquiring it may be, at least from my experience. On deity level, conquering it is often more realistic than expecting to finish it. Which brings me full-circle to the original point - I don't think it's necessary to build wonders for deity culture, but a degree of conquest likely is necessary.