Solo 401k & PEO ee's

Doctor w/own practice (no control group or ASG issue) uses PEO for all employees.

Doctor has own solo 401(k) Plan.

Doctor has not adopted the multiple employer plan for the employees from the PEO working for him so it appears they are not covered under any plan.

I'm thinking the ee's must be covered under Dr.'s plan, but not sure?

The employees are the Doc's employees, not the employees of the PEO. Think of a PEO as a fancy payroll service.  Of course they have to counted in the doc's plans!