If our games are approved, our company plans to hosting gaming in Indy for 7.5 hours each day (3 separate tables) for which we will need GMs.  I keep reading about "volunteer rewards" for GMs.  Is payment to GMs not allowed? We hope to give a stipend for each 7.5 hour shift.   Is this the best forum to recruit GMs?  I know there is an unofficial Facebook page.

You can reward GM's in any fashion that is federally & state legal I believe.  Just follow all the Gen Con policies, but they are pretty silent on what you can do for volunteers.  

Personally I give as a baseline some $ per session, shirt, and other benefits for those who run a lot of shifts like a Wednesday night kick-off dinner for my veteran GMs and core volunteers.    

Recruiting GM's is an art really.  My best results have been word of mouth and recruiting players into becoming future GM's.  You can get a few by advertising in all sorts of forums, but a lot depends on how well you market and how interesting the game and job that you are offering is to people.  Rewards are nice but I'm not seeing that as the main driver.  People want to enjoy what they are doing if they are giving up solo Gen Con time.  

I've got over 20 GM's lined up this year but could always use more, GM's are my limited factor in offering events for sure.  Good luck!

That's great feedback.  This is a relatively new game we are showcasing so I don't know any existing players attending the show.  We will make the request in this forum and others and hope for the best.