In general, one “registers” a new mount filesystem type by creating an executable mount.fstype.
$ ln -s /usr/bin/vdbfs.py /usr/sbin/mount.vdbfs
If vdbfs.py takes mount-ish arguments (i.e. dev path [-o opts]), then mount -t vdbfs and using vdbfs as the 3rd field in fstab will work. If it doesn’t, you can create a wrapper which does take arguments of that form and maps them to whatever your vdbfs.py takes.
FUSE should also install a mount.fuse executable; mount.fuse 'vdbfs.py#dev' path -o opts will go on and call vdbfs.py dev path -o opts. In that case, you can use fuse as your filesystem type and prefix your device with vdbfs.py#.