An alternative option is to install the old /dev/bus/usb in /dev/legacy/bus/usb, as it seems to be on 8.0 installations (haven't upgrade my plain FreeBSD machine yet). Then a single line change fixes our problems.
From my POV, only the "/dev/legacy/bus/usb" is fine. As we advertise __FreeBSD_kernel_version to be from 8.0 series, we should put in /dev/bus/usb the 8.0 headers.
The upstream used to have during 8.0 development these files in <legacy/dev/usb/...>, at least for brltty sufficesonly <legacy/dev/usb/usb.h> (and one line change in Programs/usb_kfreebsd.c). I will check also freeglut.
Petr