Hi
For information
Original situation:
1 DNS 320 with a Raid 1 (2x1Tb)
1 DNS 325 with a single HD 1Tb.
I switched with any problem
- the RAID1 HDs from 320 to 325
- the single "standard" HD from the 325 to the 320.
and, last but not least, the files are available

Of course, i make a backup to an external HD before to switch!
The DNS systems took less than 1 min to recognize the new configuration.
Have a nice day