Am I right in my memory that the headlight washer option could be ordered on any Camaro in 1969, RS or not? If so, on a non RS, was there a solenoid washer diverter assembly on top of the wiper/washer motor like with an RS car?

Yes there was, RPO CE1. You needed all the same stuff the RS got minus the RS headlight door system, ie, wiper solenoid, differnet wiper motor assembly, washer tubing and sprayer nozzles. If the grille is original it also had a different part number (search for the post with the PN I know it was discussed in the last 6 months or so), don't know if that part number is actually cast into the grille or not though.