No, it is not recommended to rely on data being preserved in memory during UniPHY calibration as no refresh commands are issued to the external memory devices during calibration. Only the locations with calibration data patterns get refreshed by accesses to these locations.
If you need to find out the actual address locations used in the UniPHY calibration, the recommended approach is to simulate the UniPHY IP example design for your memory IP configuration with the full calibration option.
For further details refer to the External Memory Interface handbook, Chapters :
Implementing and Parameterizing Memory IP (PDF)