The workaround is to unplug and replug the USB cable after booting the Mac. NB: There continues to be a known issue with USB UPSes under OS X where the OS power management service occasionally does not relinquish control of the UPS, leaving apcupsd unable to communicate with it. Apcupsd executables are installed into /usr/local/sbin instead of /sbin.
Mac OS X 10.11 “El Capitan” support Installer is now compliant with SIP (aka “rootless”) requirements.