One of the Korg reps replied to the harmony forums to say it isnt. (Cant find the post at the mo - HC-KSS is being horribly slow atm) They basically re-used the user interface design because they had good feedback on it, but the resulting synth is completly new hardware abd software.
I agree - seeing the two machines side by side, it looks like the radias is the next iteration of the same - they are more similar than say virus C and virus TI.
I do like the way the keyboard version is designed, but sadly korg make such f****** unbeleiveably nasty keyboards - ffs you get better keyboards in toys'r'us
