As others said, it depends on the Diner Crew or Management.
In my many years of riding Amtrak ( since A- Day), the routes I have been able to eat Scheduled meals when boarding late Trains have mostly been on the 2 night Western Routes, especially the Sunset Limited ( Tucson,Alpine, El Paso and Houston) and the Texas Eagle ( Springfield,StLouis,Longview,Dallas,Temple).
The one time that I was really surprised was on the Lake Shore Ltd. ( aka Late for Sure)when I boarded very Late in Utica and was offered Diner @ 10pm!!)
The other times I was surprised to be offered surprise Meals was in Chicago, where the Lounge gave us $$ to eat Dinner when several Trains were Delayed due to equipment problems delaying Departures, or Late arriving Western Trains making connections to the City of New Orleans caused us to miss Dinner on the CONO.