Hi Ronaldo,
could you give me a little wider description of what you are about to do?
As VX9000 is virtualized machine, you always need to think about hypervisor.
If this is in house server you need to prepare the connection to assign external IP, if this is cloud based installation, you might have this directly.
Either or, please find VX9000 installation guide
here so you can learn a little more on how to setup VX while installing or
here to find system reference guide for general release WiNG 5.8 (not sure what version you have).
If there are not other restrictions, you may assign manual IP address to your VX VLAN and have it accessible publicly.
Then you'll just pre-stage APs or let them use DHCP option 191 to find controller.
Little outdated, yet valid documentation to be found
here.
EDIT: Option 60 is not valid anymore. This is changed to WiNG. I believe.
Regards,
Ondrej