Hmm...I guess it would start with the purpose of the definition. If it is for who needs training, who should be classified in a job series, or just broader theoretical.
As a former program manager, I didn't consider myself part of the acquisition workforce. But I knew I needed to get acquisition basic training. I considered myself part of IT or PM workforce
To me there's core acq workforce - COs, COR/COTRs
And then there are others that are important as either the customer (who gets the goods/services procured) such as PM. The problems with this part is it can go really broad as most government employees are involved in some purchasing process whether training, office supplies, travel cards, etc.