In order to answer the question, one must understand the terms instinct and reason.
Instinct is natural (or intuitive) way of acting/thinking. Reason, on the other hand, is one's ability to think, understand, and form judgments through logic (reasoning).
Therefore, one's ability to be instinctive does not rely upon any thought process. For example, if a sudden thunderstorm begins, one's instinct is to run to any shelter. If one thinks about the storm, begins to reason, they will consider the different shelters available. A reasoning person will not choose a metal building over a wooden one based upon the fact that they know lightening has a better chance of striking metal over wood.
That being said, one can completely decide upon whether or not they agree with General Zaroff regarding the following statement: "Instinct is no match for reason."
I would tend to agree with General Zaroff. The truth behind the statement is realized when readers come to accept the fact that Rainsford was only able to survive General Zaroff's game of cat-and-mouse. It was Rainsford's ability to reason (to use the traps, to use his expertise against Zaroff, and to (ultimately) win the challenge). No animal, who lacks the ability to reason, could have ever defeated Zaroff.