If you add a Mac to the domain it is there for Network users from your windows domain only, it won't use any GPO's from your DC.
With your Mac mini server, if there is no risk involved and no data to be lost, would be worth updating to the latest OS X (10.10.4 Yosemite) and install Server 4.0. With this setup you can that setup policy's to control the PC. Not too difficult to set up just needs tinkering with if not done before! Be warned tho with pushing profiles to the macs and the server the network ports will need to be open for all apple traffic otherwise you won't get any profiles to a device!
Hope this helps
