To clarify: It sounds like you have a flight out of Amsterdam which departs 8:30 am. And you are looking to take a train from Berlin to Amsterdam late night/early morning on the day of your flight, and you want to sleep on that train?
Is your flight out of Amsterdam your international/trans-Atlantic flight home to the USA?
If so, you might consider the consequences of missing your flight out of Amsterdam (like, if you don't make it to the airport in time for your flight, you could easily have to buy a new ticket on the spot, which can be stunningly expensive).
Many of us are risk-averse when it comes to a scenario like this, and would plan to spend our last night closer to the departure airport, rather than in another city further away. Sure, there are lots of ways to get from Berlin to AMS (and most of them are quite reliable), but if you're choosing a night train, then a problem with that train/bus/whatever could delay you more than a few hours, putting your flight home at risk.
If it were me, I'd travel from Berlin to Amsterdam the previous day, allowing plenty of buffer time in case of a rail strike, bad weather, road traffic disaster, etc.