No, they are not the same. Unrelated AME comes from the feature. Related AME comes from the FCF and its datums. For instance, imagine a feature of size with a Position and Perpendicularity callouts. You would have 1 UAME, and 2 RAMEs (1 for Position, and 1 for Perpendicularity).
Often when someone (or the standard) refers to simply the AME or actual mating envelope they mean the UAME (unrelated actual mating envelope) and are used interchangeably, but they should really be more specific and use the full term UAME if that is what they mean.
As mentioned above the UAME is UNRELATED to any datum features. The RAME is of course different and is RELATED in orientation and if applicable, location to the datum features specified in an FCF.