I recently bought my a MGE Elipse 600 UPS.
So, of course I immediately installed it an connected my server at home to it.
After everything was up and running again I installed nut (/usr/ports/sysutils/nut & nut-usb), Connected the UPS to my system via the serial port.
All seemed to work fine at first, but soon enough nut started broadcasting messages that my ups was on battery while it wasn't.
So I connected the USB console cable instead of the serial one, but as soon as I started nut, it came back with this error: "No matching USB/HID UPS found". After a searching google for a while I found this article which solved my issue.

So in short, to get the ups management working with USB, do the following:
1 – Remove "device uhid" from your kernel config.
2 – Recompile your kernel
3 – mkdir /usr/ports/devel/libusb/files
4 – put this patch in /usr/ports/devel/libusb/files
5 – portupgrade -f libusb

You can find my nut configuration files here.
Enjoy.