No need for this to turn into a pointless debate guys. No one asked for opinions of OSX as a gaming platform, and honestly I doubt they're interested.
No way of playing DCS natively on OS X - As mentioned above, look into Bootcamp for your friend. It's already built into the machine under the Applications/Utilities directory. You need a copy of Windows to install on the partition it creates.
DCS is very system intensive however - Ensure your friends machine will be up to the task. A lot of the higher spec machines (27" iMacs, Mac Pro, 15" MBP) should be fine.