Niklas, by DNS discovery for APs, are you referring to "Method 3: Register the Controller with the
DNS Server" on the "vSZ Getting Started Guide for Release 3.2"?
If you use DNS you dont have to configure DHCP. You can either use DHCP or DNS. After you have the A-record pointing towards the vSZ you need to open all the relevant ports on the vSZ side. Chapter 8 in this document describes what you need to know : vscg-3-2-1-getting-started-guide-final. I also found the ports needed in this document: vscg-3-0-3-carrier-administrator-guide on page 395. It is an old document but those where the ones i used when I installed our vSZ.