After doing some extensive work with PlayFab / Google Sign In it looks like everything is working pretty well aside from one defect.
PlayFabs LoginWithGoogleAccount method expects a ServerAuthCode to be set. The problem here is that for iOS the default behavior is to only return a ServerAuthCode on the very first sign in attempt. All subsequent attempts will no longer return the ServerAuthCode.
This leaves me wondering how were supposed to sign in with google via PlayFab for subsequent google sign in attempts when the ServerAuthCode is not returned.
The only thing I can think of now is always signing out the user then resigning them back in to get a server auth code on ios. The issue here is that it's a bit cumbersome to have the user always have to select their google account every time they open up the game.