The debates over dates of migration have definitely changed and for the most part been pushed back later with less gap between initial settlement and later arrivals. This has had the effect of stressing the ability of the settlers to transform the landscape in dramatic fashion from being nearly barren in terms of edible plants to a place of rich agricultural production. This is further highlighted by pre-contact population figures which indicate that the settler population of 100's reached 400,000-900,000 within six centuries.

As to the story of Pa'ao... I would say, yes, it is accepted and appears usually in archeological works. It does not exist in a vacuum, there are other oral traditions and histories that later movements of people and families from Tahiti to Hawaii, and there are some shared oral histories/dances between particular lineages in the two archipelagos. There will never be any sort of direct evidence or documentation in the sense that a historian might search for in an archive; yet, that's not really a problem. Representations of the past through oral traditions or oral histories- or dance, song, chant- are widely employed in understanding Pacific pasts. They are not 'history' in the Rankeian tradition of historicity, but they are not less useful in our reconstructions.

The existence of Pa'ao (and related figures like La'a-mai-Kahiki or Pili) have been commonly accepted as fact- enough so that early historians/anthropologists of the nineteenth and twentieth century were preoccupied with figuring out where they came from- as part of their desire to find a common homeland, Havaiki, for Polynesian peoples. Later writers in the mid twentieth century like Peter Buck or Beckwith injected a certain amount of doubt into the stories and imagined them more as creative myths than real representations of the past. This changed again in the 60's and 70's when sustained archeological surveys began to take place in the Pacific; Emory and Sinoto used linguistic and archeological evidence to re-present the stories of Tahitian-Hawaiian voyaging, like Pa'ao, as having tangible evidence. The advent of the Polynesian Voyaging Society and the sailing of the Hokule'a between Hawaii and Tahiti provided further evidence for the stories of voyagers between the two archipelagos in the form of 'participant archeology.' This was important because anthropologists like Marshall Sahlins or historians like Andrew Sharpe had stressed the local origins of Hawaiian society (like Kapu, etc), imagining them as internal developments unconnected to Tahiti.

Today the existence of voyaging and voyaging networks at various points in the past is far more accepted.

A solid overview of much of this can be found in the Ben Finney article, "Myth, Experiment, and the Reinvention of Polynesian Voyaging," American Anthropologist vol. 93 no. 2 (1991).