Hah. I'm going to link this in with my out there WAG's.
I have had the wag that Harry's Bonea becomes the foundation at some point via TT for the Archive. Therefore Goodman Grey's assistance in Skin Game is linked to the preservation of the Archive line. Maybe the rent Goodman Grey is paying is wrapped up in some service to this Archive construct. And since the Archive is partially dependent on some time travel loop involving Bonea, Goodman Grey 'wanted/needed' to get involved to give an assist to Harry to help keep the Archive free and alive.
We do know something big was going down in Skin Game by virtue of the fact that Uriel, an Archangel, gave up his Grace to Michael so that he could get fixed and accompany Harry on the trip with Nicodemus into Hades domain. We don't know all of what Uriel's plan was, but it had to be momentous. I mean if Uriel had died in Skin Game, per WOJL, Michael would have ascended to become Uriel. (I recall seeing a reported WOJ but not see the actual source.) So, there likely were several very big things in play. I mostly thought it was centered around Nicodemus and saving his soul. I'm wondering if part of it was also keeping Bonea out of the hands of the bad guys.