Tina Turner has denied Jimi ever having been in her band, Ike Turner in turn claimed that he even owned a guitar played by Jimi (see upi.com for example).

Jimi:
"Yeah, I came out here before, yeah. I played here at the Fillmore with Ike and Tina and Little Richard about 4 or 5 years ago" - taped Jimi Hendrix interview recorded by Gus Gossert between 10-12 October 1968 at the Winterland Arena in San Francisco.

"...all these places like the Fillmore, I played there before with Ike & Tina you know, in the good ol', you know, "do you feel alright" -days" - taped Jimi Hendrix interview with Tony Palmer 15 March 1968 at Clark University in Worcester.

Also, the liner notes of the 1967 UK Track Records lp pressing of "Are You Experienced" mentioned that Jimi played with Ike & Tina "on the west coast".

So even though Tina Turner doesn't remember it Jimi did play in the band, although probably for a very short period and so far no exact dates have been confirmed.