That's certainly the argument Thomas Keneally puts forward in his book from which the film was drawn. It seems Schindler knew jewish kids at school, and even lived next door to the local rabbi, but there is no evidence he was particulary pro- or antisemitic, just indifferent.

As to the Nazi party, Keneally says (chapter 1)

Only the Social Democrats and the Communists did not sport the badge or subscribe to Henlein's party, and, God knew, Oskar was neither a Communist nor a Social Democrat. Oskar was a salesman.All things being equal, when you went into a German company manager's office wearing the badge, you got the order.

Keneally argues that Schindler began to be disillusioned with Naziism following the invasion of the Sudetenland when he first saw the brutality of Nazi rule. (Schindler was a Sudeten German of course, a Czech citizen until 1938.)