We have been having issues loading data from GDB files so instead are creating the LayerOverlay with the data in an external application and returning it via an API. The data comes in as JSON so trying to find out how to convert it back to a LayerOverlay. The FromJson() function gives a key mismatch error so can't use that.
I think this API only can import the JSON data which is get from ToJson.
And I think you can compare them to see whether you can write custom code to convert it.