My professor claimed that in the time period of Nazi Party rising to power and the invasion of Poland, the German economy was pretty much flawless. How accurate or inaccurate is this statement?
Flawless in what sense? For the purpose it served, to build up to an absolutely inevitable aggressive war of expansion, sure. For the purpose of long term sustainability? Oh god no.
The German rearmament was paid for using every dirty trick in the big book of economics and few more so dirty no one would even write about them. The economy was constantly balancing on the brink of total collapse the entire time. Without the financial assets seized in the anschluss, the invasion of poland and the capture of France the German economy would have collapsed on its own.
This wasn't a secret either. The allies were well aware of the financial situation in Germany. They also knew that Germany could not sustain this balancing act for very long. For that reason they were reasonably optimistic about the war, expecting a static war of attrition which they knew Germany could not keep up for very long.
The collapse of Poland and subsequent fall of France changed this of course, giving Germany the assets needed to maintain the war for far longer than they otherwise would have been able to.
Describing an Economy as flawless has no descriptionary value and is a meaningless statement.