Hi,
Before entering Downtime when SUM ask to Central Instance to be isolated and have a full Backup, Dataguard should be switched off?
As you've already been aware about the option to enable Archive logs during the upgrade from SUM tool,if you enabled the option then system will generate archive logs even when your source system in execution phase & same logs will be transferred to Data Guard as per configurations of DG & Source system.
For me if you've no space constraint at your end,you could leave DG on .
Regards,