Why not just perform an in-place upgrade of your vCenter 5.5 to 6.5? Using the wizard in the vCSA 6.5 ISO, you can move your 5.5 Windows-based vCenter to a shiny new 6.5 Linux-based vCSA which will preserve your vDS configuration (meaning no export/import necessary). Or is there some reason you don't wish to do this?
Also, we have another concern about the import vDS settings on various VCSA 6.5 on the second site similarly, VCSAs are located in two sites and their PSC are configured in Linked Mode. Is it correct or not?
You haven't asked a question, so is what correct or not?