Goodman Grey is a single unaffiliated individual, his Nemfection would not advance Nemesis cause one jot.
Goodman Grey is a single individual operating at a level where he interacts with Odin, and with Nicodemus Archleone. 
Goodman Grey is one of about half a dozen beings with similar qualifications.  You know what else there's similar rarity of?  Faerie Queens.  Senior members of the White Council.  You know what's more-common?  Fallen angels inhabiting Blackened Denarii.
Goodman Grey is 
so good at what he does (undercover ops & infiltration) that he flies entirely under the wardens' radar (Harry recognizes Hannah from Warden reports, but nothing about Grey).
Goodman Grey has 
repeatedly operated with Harry Dresden -- or in his close proximity -- in order to pay Rent.
Tell me again how Grey is of no use to Nemesis...?