The kombu I've bought does appear to have a film of salt on the
surface but I find that it can be mostly wiped off with a damp [paper]
towel or perhaps you can rinse it off.
I'm sure that there is still some salt remaining in it but I would
think that it's much less than the amount of salt you'd use for
seasoning the beans. I haven't detected any toughness in the beans
when I use kombu this way.