The problem, at least in my case, appears to be a 64/32 bit mismatch between nut and libusb. Nut is built 64 bit but looking for libusb.so.2. The 64 bit version of libusb is libusb.so.3. libusb.so.2 is 32 bit only.
root: /usr/local/etc/rc.d/nut.sh start
starting usbhid-ups
Network UPS Tools - UPS driver controller 2.6.5
Shared object "libusb.so.2" not found, required by "usbhid-ups"
Driver failed to start (exit status=1)
usbhid-ups failed to start
root:
root: find / -name 'libusbso'
/usr/lib/libusbhid.so.4
/usr/lib/libusbhid.so
/usr/lib/libusb.so
/usr/lib/libusb.so.3
/usr/lib32/libusbhid.so.4
/usr/lib32/libusbhid.so
/usr/lib32/libusb.so.2
/usr/lib32/libusb.so
root:
/root: file /usr/local/libexec/nut/usbhid-ups
/usr/local/libexec/nut/usbhid-ups: symbolic link to `/usr/pbi/nut-amd64/libexec/nut/usbhid-ups'
root: ldd /usr/pbi/nut-amd64/libexec/nut/usbhid-ups
/usr/pbi/nut-amd64/libexec/nut/usbhid-ups:
libusb.so.2 => not found (0)
libthr.so.3 => /lib/libthr.so.3 (0x80075d000)
libc.so.7 => /lib/libc.so.7 (0x800982000)