This is a little outside my area, but I will take a stab at it and someone may correct me. For purposes of the deduction, a professional services firm is "any trade or business involving the performance of services in the fields of health, law, engineering, architecture, accounting, actuarial science, performing arts, consulting, athletics, financial services, brokerage services, or any trade or business where the principal asset of such trade or business is the reputation or skill of 1 or more of its employees." See Code sec. 1202(e)(3)(A). So does not seem to require a professional license. My guess is that even TPA services that do not involve actuarial work would hit one or more of the other categories, e.g. accounting, financial services, or principal asset being reputation or skill of employees. However, nothing is certain until we have guidance from IRS.
However, a lot of "lowly pension administrators" (assuming they are not W-2 employees, but sole proprietors or partner of the TPA firm) will still get all or much of the benefit, since the exclusion for "professional service firms" only applies to joint returns where taxable (not gross or AGI) income exceeds $315,000, or individual returns $157,500. Above that the benefit is phased out to 0% once taxable income hits $415,000 or $207,500 respectively.