Thanks Vern for this comment. In weighing the pros/cons of how to appropriately categorize "consultant" and whether it fall under "subcontractor", I think an argument could be made for consultants to be a subcontract but agree that the FAR doesn't specifically define or specify if this must be the case.
In considering the type of work that my Agency (USAID) performs overseas, it often generally includes a heavy reliance on "consultants" who are hired by the prime contractor to then help perform the SOW in activities such as providing expert advice to a foreign government or organization, providing consultants to do the data collection or indicators of progress, etc. Since the mechanism used is often a CPFF completion-type, and a large portion of costs incurred in these contracts relate to labor costs for consultants plus travel, I believe it prudent to exercise a level of oversight, despite the administrative burden, in mandating approvals for the usage of the "consultants" but don't believe it necessary that all the flow-down clauses are necessary.
Given the above considerations for the work and types of contracts, I think the best way forward is to leave the ambiguous "consultant" category undefined as a third category outside the employee or subcontractor categories and administer it with a special requirement in the contract for CO or COR advance written approval for each consultant mobilization with requirement of the contractor providing the objective of each consultant, period, and the total cost for review in the approval requests.
Thanks!