SSL Native V6 and Duende Native V5 can be hosted in your DAW at the same time.
SSL Native are enhanced versions of Duende Native; although they are licensed by the same iLok licenses for Duende Native, they are not the same versions.
By allowing both V5 and V6 plug-ins to be hosted in the same session, you can rely on the V5 plug-ins to continue to recall perfectly in older sessions, whilst enjoying the benefits of SSL Native V6.