I think the decom case is the main concern. I’d have to test that but you might run into some problems w/ the decom in that case.
I tested in 8.7 and the decom worked. The value of the property value just stays, but you wouldn't be able to reuse it if you remove it because the server is gone from the available choices... I'm more concerned about 8.5.
test I did:
1. Created a server property using property class Server
2. Created a dummy target server
3. Set the value of the new property on another server to the dummy target
4. Added the property as a column to the group explorer view of a smartgroup so I can see it, and filtered for the server I used as a test. I could see the name of the dummy target as the value
5. Decom the dummy target, and didn't prompt for any dependencies
6. Refreshed the smartgroup and the value stayed intact, even though the dummy target is decom
I was able to edit the value without problems...