That would be something I would test. I don't know Ceph, so I would be taking a shot in the dark. I would guess it would not make much of a difference as everything is block level. I, personally, would do 1x PCIe SSD for cache, 1x 2/4TB SSD, and 2x 4TB HDD for each storage node.

Edit. If Ceph is smart enough, it would be aware of the tiers present on the node, and would tier blocks on that node. So a Block on node A will stay on node A.