Dr.bronner's bar soap okay to wash hair with?

I wouldn't : I'm not specifically familiar with this soap, but bar soaps in general tend to be pretty harsh on the hair. In a pinch you could use it but i would generally use products made for the hair that don't strip as many of the oils out.

Sure: I see no problem with using this to wash your hair. If you do it for awhile and your hair does not seem to respond well you can try something else but this should be fine for most.