Page 440 of CMMI-DEV 1.2 model clearly states that: "SAM process area does not directly address arrangements in which the supplier is integrated into the project team and uses the same processes and reports to the same management as the product developers (for example, integrated teams)."
This statement opens room for some Lead Appraisers to trigger the default button: "SAM is out." But the paragraph continues with the following statement: "Typically, these situations are handled by other processes or functions, possibly external to the project, though some of the specific practices of this process area may be useful in managing the formal agreement with such a supplier."
In my oppinion, not considering SAM may incur problems in the future because you may be postponing the elaboration of a mature way to handle suppliers and contracts and this will be necessary when the organization evolves to higher maturity levels. And, of course, it will be necessary to survive in a global IT world driven by strong and stronger supplier/acquirer relationships.
In my country, only 2 out of 16 organizations who published their Maturity Level 2 appraisals considered SAM in their scope. And, guess what? Many of these organizations use a high number of contractors in their development phases. So, what led them to exclude SAM?
It is important to understand the intent of SAM. If you are augmenting your staff by having a supplier provide people and these people then act, for all intents and purposes, as your employees, then SAM does not apply. Basically, they are following your processes and not managing any of the work on their own, you are managing the work. However, if you give the supplier a chunk of work that they can manage by themselves using their own processes, then SAM applies. So both the organization and the Lead Appraiser need to be aware that if the relationship changes with the supplier, then SAM may move from being N/A to in scope for an appraisal. And you raise a good point, whether or not the Lead Appraiser determines if SAM is in or out of scope, the organization should be aware of the necessary practices it should have in place to manage a supplier.
And if the organization wants to become more sophisticated in managing suppliers, they should be using the CMMI-ACQ.