No, it's against the RAW as the restriction is mentioned in Your World several times.
Not everything in Your Story and Our World is a rule, you know. Both books are full of stories and setting bits.
(Incidentally, which one did you mean?)
The main reason for looking into playing a true or pure fae was to beable to have a Pc with greater glamor. the rules i have say you must be pure fae to have this power. which suchs mainly the power looks fun but does not really look to over the top on power scale.
Pretty sure that's backwards reasoning.
I strongly suspect that the Power was restricted to true fae purely to prevent PCs from having it. If you want to take it, make it suitable for PC use and forget about the restriction.
Powers can only be taken by characters with suitable High Concepts anyway, so if you believe that Greater Glamours isn't suitable for dream spirits or whatever then the restriction is redundant.
Making the Power suitable for PC use pretty much just requires a ten minute chat with your GM on the topic of what exactly Greater Glamours does. (Can I make a super-tough True Seeming and have it beat you up? Should I roll dice to see?) The solution you come up with will probably be vague and in no way suitable for mass use, but at your table that doesn't have to matter.