I would think any savings would likely be lost to paying the sales tax twice. (Assuming they are not a dealer- they would pay it on the new car and you would pay on the used) You would also have issues with financing, trade ins, etc. If you supply the money to buy the car in their name, you need to trust they will transfer it back to you- their name would be on the original title and it would legally be theirs. It's probably not worth the hassle.
The GM employee or supplier can give you one of their discount codes. They don't have to buy the unit. They will require your SS# when they call in for the code. I bought mine with a GM employee discount from a friend that retired from GM. Just be sure you trust the person before you give them your SS#!
I might be wrong, but I think that the pricing is something like this.
Supplier - Over invoice, but under MSRP. If I remember correctly, it is about 1000 over invoice for the Acadia.
Invoice - The dealer invoice price with is a few percent over what their actual bottom line cost is.
Employee Discount - Usually a few hundred under invoice.
I bought my Acadia for invoice - my discounts. I would think you could do better than supplier price just by negotiating.