I would not hesitate to say that Jackson > Gavin in creativity. Again, I have no reason to be biased against Gavin, since he's in one of my fave bands ever.
Haven't heard his outside-of-Porc-Tree stuff, no. But I guess my philosophy is, someone who's well versed in jazz ought to bring all that creativity into rock anyway and be able to be reasonably evaluated talent wise (creativity wise) on the basis of their rock work. You don't need to listen to Bruford or Carey's jazz work, or Reinert for that matter, to know they're something special: they bring that 'special' into their rock playing. So I'm skeptical that listening to Gavin jazz would raise my opinion of his talent/creativity that much, but who knows.
I'm not saying Gavin isn't creative btw. I just don't think he's on the level of Al Jackson or Danny Carey. I do think he's one of the more creative rock drummers ever. But creativity and innovation are two different criteria and while he may be absolutely nuts in innovation, I don't think he's quite at that level in pure creativity. What's he done that touches Heart of the Sunrise, or Indiscipline, or South Side of the Sky, or A Day in the Life, or She Said She Said, or Good Times Bad Times, or Won't Get Fooled Again or...
You need to check out his stuff with 05Ric.