This response is based on the information provided.  We suggest you discuss with your contracting and finance team, program manager and/or legal department as appropriate.

There no comprehensive definition of Base Operation Services (BOS).  What defines BOS can be different from one unit to another.  Commodities are not services, but there are many other items that would not be considered BOS.  We suspect the question is not the definition of BOS so much as the host base trying to manage workload.  We suggest a conversation with the host base to understand what is driving its concern about providing continued support.