While I cannot speak for Greg's current role in GC(whatever-it-is-this-week), he moved to Orlando in 2001 when the national office relocated there from Columbus/Worthington, OH.
My understanding was that Greg led Rob Schiller to Christ, and was part of the "early group."
I don't know the precise nature of the arrangement, but I do know that as recently as several years ago, many GCM pastors were "accountable" to Greg (I don't know what the nature of that accountability was/is). Also, after Jeff Kern stepped down as leader of the movement several years ago, he was replaced by a trio of individuals. I remember Greg's name coming up at that time (perhaps as head of gcac???), but I don't recall if he was actually one of the trio in question. I'll have to do some hunting on that one.

While I've never been close to Greg, the times I met him, I was extremely moved by what a gentle man he is. The times I've met him, he was a stark contrast to some of the more "gruff" leaders/men in gcm.
I was also impressed by what a humble, godly individual he is. In my experience, humble men aren't the ones who go around shouting from the rooftops about how humble they are, nor are they the ones giving sermons on how one can be more humble. Greg led by example.
Ahhh....did some quick hunting....
Greg is now the US Churches director:
http://www.gcmweb.org/about/meetteam.asp?section=28