Hello,
Please refer to the following article: http://www.symantec.com/docs/TECH104389
Add MACHINE_1 under Priority 2 and add MACHINE_2 under Priority 1, and assign this New Management Server List to all the groups.
To answer your question, the SEP clients contact the SEPM using the IP address.
So, as long as your client machines are able to contact the new server on the installation port and IP address of the server, the migration should be fine.
Secondly, just make sure, that your DNS resolves the server name to the new IP after all. you can always try and bring it back to the old vlan.
Hope that helps!!