I run a solo practice so I am involved with the cumbersome requirement of CLIA.
Mohs surgery is considered a high complexity test and thus the Laboratory Director needs one year of path during the residency training. Dermatology is the only specialty that qualifies. My guess that it is conceivable that an ENT or Plastic join a derm group or path lab work in their office to bill under their High Complexity CLIA laboratory. But there is no way for ENT/Plastic to setup an ancillary lab in their own office unless they get additional path training. That is probably why it is a handful of Plastic/ENT doing Mohs rather than an army of them.
It is under the same logic that derm can process their own slides in their office and get TC from Medicare. Derm can have their own in house ancillary CLIA certified lab.