I have developed an ArcGIS map using the ArcGIS SDK for Javascript (v 4.30). The Nearmap aerial map service must be integrated into this map. (The Nearmap tool, available in the ArcGIS marketplace, allows you to integrate Nearmap with ArcGIS online. )
I would check with Nearmap for any specific questions, especially if these services are secure and you need an API key or something to access. It looks like they have both WMS and Tile services available https://help.nearmap.com/kb/articles/360-getting-started-with-nearmap-apis so you should be able to either bring them in to your app as a WMSLayer or TileLayer.
@Sage_Wall Thanks!