You can't mix them at all in the same member.   You can't create a new RAIDset using SED drives alone.  Those drives have to be added to the existing RAIDset.    Each member array can only have one RAID policy and it will use all available drives. 
We have recently purchased new disks from Dell. However, all the added disk are shown as foreign disk. We followed the instruction to add to RAID and allow clearing data. Within a few seconds, the status changed to spare and then back to foreign disk. What could be the problem?
PS4000 unable to clear foreign disk label