[quote=@NecroKnight]
[@VKAllen]

Sure. 

Yet keep in mind Yuna, has propagated her 'condition' - that likely even Ferghus wouldn't know if she is really blind or not. 


[/quote]

Medallion would give her away. Not just that, his own medallion would react if they were close (in proximity). Her training and proficiency with blades and witcher hunting techniques would give it away too.

EDIT:

I will acknowledge the fact that if you wish that he has travelled and did contracts with her. If she did not and never met him and only heard of each other through word of mouth, he would not have known.