If it is indeed Fulgrim, and there's no good reason to think otherwise given what Trazyn says about earlier opportunities, he's definitely happy to play dress ups with his man-dollies. The original description I recall was of a giant in baroque armour and as I recall, Clone Fulgrim wasn't wearing any real armour at the time Fabius handed him over. Not that it's all that surprising, given what we know of his habits...
I'm looking forward to the next entry in this series, which is apparently due out later this year - I've really come to enjoy Fabius immensely as a character through this series, despite the fact that he's awfully deluded about his ownership by Slaanesh. Maybe he still has free will, but he'll never truly be free.