An AGWA version for ArcGIS Pro has not been released yet, and ArcMap add-ins are not supported in Pro, so Esri tech support is correct. AGWA 3.x versions are only for ArcMap 10.x. An AGWA version for ArcGIS Pro is in the pipeline but is missing a few features that are holding back its release. Be aware that when AGWA is released for ArcGIS Pro, only the KINEROS2 model will be supported initially, followed by RHEM. There are no plans to add the SWAT models to the ArcGIS Pro version.