Can ArcGIS Hub be migrated to ArcGIS Enterprise?

No, as there is no tool to completely migrate an ArcGIS Hub site to ArcGIS Enterprise. Although the site itself cannot be migrated, the contents of the site can be cloned and moved to ArcGIS Enterprise using ArcGIS API for Python. Refer to How To: Copy/clone content from one ArcGIS Online organization or Portal for ArcGIS to another for instructions. After the items are copied, rebuild the ArcGIS Hub site by using the migrated content in the ArcGIS Enterprise portal.