Thanks Dan. It turns out that this does work in 2.4.2, but you have to have the uri for the ImageServer exactly right. I added the ImageServer to my project in Pro. When I tried to run the clip tool, I clicked on the folder icon to navigate to the image service that I wanted to use. This is the string that populated the Input Raster field: C:\Users\lbross\Documents\ArcGIS\Projects\MyProject1\arcgis on serverName\DAILY_SWE_NORMALS\daily_swe_normal_apr_01.ImageServer. But apparently the GP tool cannot address the image service in this format.
I went back to ArcMap and retrieved the url that had worked previously: http://serverName/arcgis/services/DAILY_SWE_NORMALS/daily_swe_normal_apr_01/ImageServer. When I pasted this into the GP tool, I did not receive an error and the clipping worked! I hope that this works with the Pro SDK which is where I'm actually hoping to use it.
As an aside, when you're doing ArcDevelopment, it's not super easy to upgrade to the latest version. I have to keep my add-ins and my Python scripts in sync with what my users are using. These frequent releases of ArcPro will take some getting used to.
