As seen in a recent announcement, Bentley SewerGEMS V8i SELECTseries 5 (08.11.05.58) has been released, which adds support for Esri ArcGIS 10.3.
An update is also now available for Bentley WaterGEMS and HAMMER V8i SELECTseries 5 (08.11.05.61), to add support for ArcGIS 10.3.
Please see the below article for some important details:
Integrating WaterGEMS, SewerGEMS and HAMMER with ArcGIS 10.3