Can a TPA provide DOT follow-up testing schedules to an employer?

No, as per § 40.355 - What limitations apply to the activities of service agents?

Except as provided in paragraph (h) of this section, you must not make decisions to test an employee based upon reasonable suspicion, post-accident, return-to-duty, and follow-up determination criteria. These are duties the actual employer cannot delegate to a C/TPA. You may, however, provide advice and information to employers regarding these testing issues and how the employer should schedule required testing. Paragraph (h) deals with owner operators.