Looking thru a few of their web pages, I can’t find anything that says which railroads they actually service. They always seem to refer to their airline experience. They seem to be associated with Lufthansa, so maybe they are on some German/European trains?
A quick look suggests that this firm would be well-suited for supplying snack bars, galleys, cafe cars, etc. Food service cars like those are not that different from airline food service. Full-service dining cars would be outside their realm of expertise.
I don’t think they cater the food service on Deutsche Bahn. As to their airline food, the coach food on Lufthansa transatlantic is quite good and business class better than Amtrak’s full-service dining.