Janis Joplin and Jimi Hendrix were two early Hippyraver’s back before
many even knew the term and certainly might have played together, Youtube has many videos posted claiming that Jimi Hendrix played guitar in them with Summertime being of them. Since we can’t ask either, we just have to go with our instincts, the sound of the song and the Youtube comments under the video.
The evidence is:
1. Nobody thinks Jimi sounds is present
2. Janis had great backing band the Holding company and it sounds like them,
3. Way more commentators believed it was not Jimi.
Using ockham’s razor- The most obvious/simple answer wins, we go with the NO, however it this version of Summertime is amazing and you can enjoy Janis play it now.