I have the following in an environment using split DNS:
2- Exchange 2013 DAG (Both MBX and CAS roles) EX1.company.com & EX2.company.com
1 - DAG - I create a DNS entry to point mail.company.com to it's IP
1 - Witness Server
I basically followed this: http://exchangeserverpro.com/installing-an-exchange-server-2013-database-availability-group/
If I currently launch OWA, by going to mail.company.com (which goes to the IP of my DAG), I can get to OWA it works fine and I can shut down either Exchange server and it continues to work.
Now I want to know how I should setup internal and external URLs of all the virtual directories. Should I point everything to mail.company.com? Right now I have internal setup to EX1.company.com (or EX2.company.com) and external mail.company.com. Internally everything is working fine, but externally I have clients connecting to EX1.company.com instead of mail.company.com, after using autodiscover.
Obviously there was much more configurations, so if you need further information, please let me know.
Ryan