Great question Pastor Dave. Are there other trains other than the Downeaster have the outsourched system? Somehow I would be surprised if there was but you never know...
I've ridden quite a few Amtrak routes and never considered "outsourcing" as one of their strategies. I guess from a business perspective it sometimes makes sense but, none the less, those folks would still represent Amtrak and have an impact on Amtrak's reputation.
BTW, as a regular Amtrak passenger I do notice deficiencies at times and can usually overlook them. Rudeness however usually at least has me sending Amtrak a letter.
Outsourcing isn't one of Amtrak's strategies.
The Downeaster is a state sponsored service. The State of Maine setup the NNEPRA (Northern New England Passenger Rail Association) to oversee and pay Amtrak to run the Downeaster. As such, they have the right to tell Amtrak what to do and essentially, at least within FRA laws, to run the train. NNEPRA choose not to use the normal Amtrak commissary, as well as to not use an Amtrak LSA to run the cafe car.
I believe that the Downeaster is the only state sponsored service to actually use non-Amtrak personnel to run the cafe car. However, both California and Oregon/Washington do dictate what gets sold in the cafe cars on their state sponsored services. I believe that the food still comes from the Amtrak commissaries, and via that from Aramark, but it is possible that a different caterer was chosen. I'm just not sure.
And North Carolina dictates what gets sold on the Piedmonts, but I believe that the Carolinian is just run as a normal Amtrak train. Wisconsin/Illinois don't pay for full cafe service on the Hiawatha and only provide a cart based option. And Pennsy doesn't pay for any food service on the Keystones, so there is none.
I'm not aware of any other diversions, other than VIA's operation of the Leaf as noted by Wolverine, but that's not to suggest that there isn't.