To be honest with you, I don't think there was a specific prototype for the hustler. it is just a small industrial switcher that Athearn came out with. There are other similar prototypes, but I don't think anything EXACT.
The hustler was meant to be an industrial switcher. it would be found switching small industries, or large ones too. They would have been owned by the industry, not a railroad. So, if you have any industries, you could letter the hustler for that, or a "leasing" company. If a large railroad had small loco,s like that, it more than likely would have been used as a SHOP switcher, or a loco used to switch loco's at the engine facilities.
Hope this helps