Is an Inherently Governmental Determination required for commercial acquisitions using Part 12? Can the contracting officer say the requirement from FAR 7.503(e) does not apply to the commercial acquisition?
Correction: The quote from DODI 1100.22 4.c states "Functions that are IG [excludes "not"] cannot be legally contracted.
Your overall logic is flawed. Just because "functions that are inherently governmental are commercial in nature" does not mean that no commercial service can be inherently governmental. A job description for a commercial service could be written to make it de facto inherently governmental. For example, the broad category of professional and consulting services can meet the definition of a commercial item, but the work statement for the acquisition may be written (mistakenly) to include inherently governmental roles and responsibilities. So no-- a contracting officer cannot say FAR 7.503(e) does not apply to commercial services. Also note that the "Applicability" section at FAR 7.502 does not exclude commercial services.