How much of the late 90s boom was Hogan? I think an argument could be made that he was 2nd or even 3rd in terms of NWO popularity, and that the third man could've been someone else & still been successful. Hogan wasn't that big a draw in the 90s. His babyface run in WCW wasn't as big a success as Bischoff and Turner had hoped. Aside from Hogan, there were other factors just as important, if not moreso, in the NWO's success and the boom period. The decade was marked by 'alternative' and 'outsider' -ness. It was also a decade of the rise self-referentialism, as seen with Seinfeld. Hall and Nash were charismatic and fit the tone of the moment perfectly (which Hogan did not). DX was popular; if HBK (who also fit the mood of the moment) were the third man, I think it had a chance to be just as successful as Hogan.
Those were also the factors of the WWF's comeback and its place in the boom. Steve Austin was the outsider fighting with his boss. It jibed with Seinfeld, South Park, the Sopranos, etc. Stone Cold probably doesn't happen if McMahon just relies on aging stars. He needed something totally different and Austin was it.
The late 90s boom didn't need Hulk Hogan. Or the Ultimate Warrior or PG Piper or etc. Those types could've still had a place in the boom. But they were not required. Hogan didn't need to be the third man for it to work. But tying into the mood of the moment and the state of pop culture in the 1990s was absolutely essential. HBK could do that as the third man. The relics of the 80s could help put stories and guys over. But without the rebel attitude, the alternative style and ethos, or the 'cool' factors of that particular moment, the boom would not happen.