I was a big rock fan during the late '60s and I do not recall any of those three (Hendrix, Joplin, Morrison) ever saying a word about Vietnam. Certainly not like David Crosby or John Lennon, to name just a couple of the louder anti-war activists.
Morrison got a lot of grief for the song "The Unknown Soldier".
The debate still rages over whether the song was simply tragic, sentimental imagery or anti war.
*shrug*
It works both ways.
Yea , Hendrix was anti-war ..Machine Gun ???