On FreeBSD, devd has a similar role to udev on Linux. The devd.conf file
defines actions to perform when devices are plugged in.  

The tools/nut-usbinfo.pl script generates nut-usb.conf.in by processing USB
macros in all of the drivers. In this case, the defined action for each
matching UPS is to change the permissions such that the NUT drivers can access
the devices without requiring root privileges. You may need to restart devd and
re-plug in the UPS to trigger the actions.

The format of this configuration file should work with devd on FreeBSD 9.0 and
9.1, at the very least.