Here's info pasted from my favorite link found:
Amtrak People
Service and Train Crews: The Amtrak personnel are divided into Service Crew and Train Crew.
The service crew includes Car Attendants (not called "porters" please), Snack Bar Attendant, Lead Service Attendant (LSA; head waiter in dining car, and in charge of all service crew members), Dining Car Chefs, and Dining Car Attendants (waiters). Service crew members generally ride the train from origin to destination.
Operating crew includes the Conductor, Assistant Conductors, and the engine crew. Train crew will change about every 6-8 hours on long distance routes. With very few exceptions all crew members are Amtrak employees. The Conductor is in overall charge of the train.
--------------------------------------------------------------------------------
Tipping
General Guidelines: Tipping is NOT required, but is considered correct for the service crew personnel on the train. Recommendations: Snack bar attendant: roughly 10%. Dining car: 15% of menu prices (sleeping car passengers may want to note this when ordering their meals). Coaches: the consensus is that in most cases tips are not necessary, but if special service is given, the guidelines for a sleeping car attendant apply. Sleepers: See the next section. Operating crew is never to be tipped.
Tipping a Sleeping Car Attendant: The sleeping car attendant that will greet you when you board the train will be with you throughout your journey and will be changing your room configuration at least twice a day, and performing other services, so it behooves you to get on their best side -- and they on yours. Here are your options for tipping a Sleeping Car Attendant:
Some people recommend tipping the attendant at the first opportunity -- say $20 for what will be a 2 night trip. The idea here is to "pay" for a good level of service up front, to possibly give you a leg up on other passengers, so to speak.
Others say one should wait until the trip is over and tip according to the level of service provided -- if for example you hardly ever saw the attendant and they did nothing much for you beyond the absolute minimum, then no tip or a very small one is appropriate.
Others suggest tipping the attendant in the morning if the service over the past day or part of day has been satisfactory or better. $5-$10 is appropriate.
Others (yes. there are some) suggest that Amtrak Sleeping Car attendants are not at all badly paid for their hours of service and thus should not needed to be tipped at all.
You could pick any of the options above and not be "wrong".
Personally, we believe tipping is appropriate, and don't recommend the fourth option. We go with the second one -- tip at the end according to level of service. For reasonable service for (say) 2 nights for a couple in a Roomette, we would tip $20. This is probably the most popular option of those above -- though many people just never even think of tipping the attendant.
We also go out of our way to be friendly to the attendants and helpful to them in whatever way we can -- basically to treat them well. Our experience has been that a big smile and friendly greeting gets one that little extra without any need to promise compensation up front.