The marks on the mystery member's cheeks are likely just showing that he has dimples or rosy cheeks (like chao). That being said, its possible that he is fate and not fate.
Eva said Fate was a construct remember? So its possible that Fate is a doll created by this mystery member.
Its also possible that the mystery member was the blond female that guided Negi and Co. to the magic world. Unless im mistaken.
i think the mystery member is the person with fate. look at the picture and look cap 209 pag 15. look to the bottom, in the right. He looks like with the boy in eishun's picture
I have reach the conclusion that the mystery member was a tomboy. The dimples on the MM's face is one way to identified him as a tomboy. The MM seem not to have shown up with Negi, Eishun, and Al during the Battle of Ostia. Yet, there is an unknown young female mage on a broom in Asuna's flashback of the battle. To me, the female mage was leading Al, Eishun, and Nagi to where Asuna was.
Since the MM was likely the intel officer of the Al Rubra, he had to be the young female mage on the broom. Being a tomboy, the MM was able to disguise herself as a female servant, in order to inflitrate rhe ene'my's camp.
Rakan had known that there were two other members of the Crimson Wing/Al Rubra.At the time when he told Negi, he seem to have forgotten Al 's and the MM's names.
Rember, my conclusion about the MM being a female is my own. It is up to Ken to identified the MM. If he did turn out to a tomboy, there is a chance that the MM is likely Negi's mother.