Linux how to determine the file system type of unmounted (raw) partition

Of course!
You can try a ‘file -s’ on the device node.

root@rescue /mnt # file -s /dev/md1
/dev/md1: Linux rev 1.0 ext4 filesystem data, UUID=e77cc8ce-ade6-4e09-ac7f-d139c80a2e4a (needs journal recovery) (extents) (large files) (huge files)
root@rescue /mnt #