Again, this issue is only related to the 410(b) test for coverage.
I am saying that if you have each person in their own rate group, and some folks get zero because the employer chose their rate group to be zero, then your coverage test for the 'plan' must pass using the 70% ratio percent test described in 1.410(b)-2(b)(2).
Further, please note that I am saying that, in my personal opinion, any "reasonable classification" must be accomplished at the plan document level, and a document that says "each in your own class" is not based on any of the objective business criteria that you see listed in Treasury Regulation 1.410(b)-4(b).
Thus, if you have each person in their own rate group, and the employer says "all hygienists get zero", then that still does not make it a reasonable business classification, and thus the ratio percent test is still needed for coverage and the plan cannot use the average benefits test for coverage.
if the plan document listed "hygienists" as excluded from the plan, and if that is a reasonable business classification, then the plan could try to pass coverage using the average benefits test if it needed to do so.