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I just recieved a response from Esri Australia who stated:
"Unfortunately 9.3 is not supported with the current release at 10.2. However, I have been able to check on MyEsri with the ArcGIS 10.3 prerelease products, and PostgreSQL 9.3.5 is currently supported with the 10.3. prerelease. Reference: https://my.esri.com/#/downloads/ArcGIS%20for%20Server%20Enterprise%20(Windows)%20(Prerelease/10.3
ArcGIS 10.3 Prerelease is available for download to all customers current in maintenance."
I do not see any changes to the 10.2 System Requirements page as of yet, but for 10.3 prerelease the following link can be referenced as a guideline:
Use these system requirements as a guideline for planning purposes as they are subject to change before the final release of ArcGIS 10.3.
Minimum supported database versions
PostgreSQL 9.1.13 (64-bit)
PostgreSQL 9.2.8 (64-bit)
PostgreSQL 9.3.4 (64-bit)