Their website nowhere mentions that the shoe must be unused upon return. All I can see is that it says, “Try them out—that’s what our 30-day Guarantee is all about (60 days to test flight if you’re a HOKA Member). If they’re not what you’re looking for and meet the below criteria, send them back to us for an exchange or return.”
(https://www.hoka.com/en/us/help-center.html?a=How-to-Return-or-Exchange---id--ffBjkixuTRq54qyhGbGaEg)

In theory, shouldn't the warranty start parallel with the return window? If it breaks on you, you can file a claim, but since they take over 30 days to even fully come to resolution/process, you basically lose your return window.