The rescue image contains all the needed drivers. SuSE
just forgot to link the
initialization script /sbin/init.d/boot.device-mapper
into /etc/init.d/boot.d . If you run the commands
manually after logging into the rescue system, you should be able to mount
your LVM filesystems.
IIRC that was intentional because the LVM start scans a lot of
devices to discover all PVs and that can cause problems in tricky
rescue situations. Admittable it should be better documented,
although the rescue disk generally requires an experienced user.