TMG2010 - Exhcange 2010 - Restrict User Groups

Hey Guys, 

We have TMG2010 currently reverse publishing OWA however no Pre-Auth is being used, the Exchange 2010 Auth Form is being used. 

The TMG box is not Domain Joined, however if we joined it to the domain would we be able to use AD Security Groups to restrict access to certain services such as OWA?  Without enabling the "Pre-Auth" Functions of TMG? 

Thanks, 

Robert 

Robert