Is it acceptable to use USB connectors in non-USB applications?
This depends on your situation, and what the failure modes of plugging a USB cable into your device would be.  When people see a USB connector, people want to plug a USB cable into it.  A decade of user experiences confirms this behavior as valid.  If it makes no difference, and your device can laugh at 5V coming in on the USB pin, and you won't kill someone's laptop in the process, you should be OK, but your users might get confused.