I just ran the ESMC upgrade on my old ERA Server. After that I ran the Security Management Center Components Upgrade as well as an Update for the Rogue Detection Sensor
Now the ESMC Reports that the Server has the following installed:
Remote Administrator Agent 6.5.522.0
Remote Administrator Server 6.5.522.0
Management Agent 7.0.553.0
Security Management Center Server 7.0.553.0
Rogue Detection Sensor 1.1.693.0
I do see the previously specified Registry Entries for the ERA Agent, as well as similar entries with the ID FF4A76B03E71D144183AEA3C39576B29 for the ERA Server.
So I would guess that while the upgrade was successful (it does Show me the new GUI at least, and I suppose it wouldnt really work with both versions actually installed) the same uninstallation error can also happen with the ERA Server.