A parts department is there for you to buy parts from, not be a vehicle encyclopedia.
Here's the problem with calling the parts department for fluid specs. When they look up the fluid in the catalog, often times they will get a generic description like "Fluid, Transmission" and the part number. There may be a description, but it's not a guarentee. Now, if you're simply there to buy the correct fluid, they go back into their stock and grab a couple quarts. You walk away with the correct trans fluid. You weren't there to buy parts though, were you? You were just using them as a resource to find information, then you were going to buy the fluid someplace else, once you knew what it was. Is that about right?
I just looked in the parts catalog. No, there is no identifier about what kind of fluid it is. The fluid spec is listed in both the service and owners manual(yes, I just checked these too), so it's not as if GM was trying to hide anything.
As an "Automotive Service Technician," I would suggest you invest in some type of online service information that will get you the information you need to best serve your customers, rather than relying on phone calls to the dealer parts deapertment. A 15 second search in AllData found your answer.