Technician a says that shims are sometimes used to adjust camber. technician b says that shims can sometimes be used to adjust caster. who is correct?

I'll have to be honest with you.  I've read both of those opinions several times, carefully, and it looks to me like both technicians are saying exactly the same thing.

Now, my knowledge of shims and camber is limited (to approximately zero), so all I can say to answer the question is this:  If EITHER technician is correct, then they're BOTH correct.