Thank you for your question.  I agree with the position you are taking.  The prescription for FAR 52.204-7 is found at FAR 4.1105(a)(1) which is what you need to read to determine if the provision goes into your solicitation or not.  As a result, like you, I don't think it is based on whether or not FAR 52.204-8 is in the solicitation or not.  Therefore, as you alluded to in your background information, "when the provision at 52.204-7, System for Award Management, is included in the solicitation, [you] do not separately include the [34] representations and certifications [in the solicitation]."