I have a few AGSArcGISVectorTiledLayers downloaded to the phone and normally we show it on a Basemap of our own. We're trying to see if it's possible to show the layers on an Esri Basemap. The problem we're running into is the Basemap's spatial reference WKID is different than the layers. Is it possible to do what we're trying to do?
Unfortunately, Runtime does not support reprojecting vector tile layers on the fly. You would need to republish the vector tile layers in the same WKID. Note that we do have some WGS84 basemaps, in case that's the reference of your tile layers.
If you're using vector tile layers to present features from a feature service, note that you could use Feature Tiles. This was added to Runtime at 100.9. It balances the speed of static vector tiles with the content of features.