Yes, it is a potential problem in that you're changing the IPs, however with a little careful management you'll be fine for a very quick cutover.
The three critical things that occur to me are:
(1) - Use the "rinetd" daemon (install from source) on your old server to transparently forward access attempts to the old IPs to the new IPs;
(2) - Edit the DNS zone files (/var/named/*) to change all the IPs to point to the new server
(3) - [optional] 24 hours before changeover, reduce the DNS zone TTLs (/var/named* as above) to be something like 600 seconds. This won't present much of a load on your server (DNS packets are tiny) if you have a low domain count - although be warned that if you host over 2000 domains on that server, you may have a problem with DNS load (actually over 3000 - but you may be alright).
Don't forget that if you have Child DNS IPs setup at the registrars, you'll need to change those or some of your DNS requests will end up being aimed at the old server.
The rsync script posted in the thread referenced above will be a factor of 10 times faster than copying accounts with cpanel or restoring cpanel backups. Don't forget to edit the nameservers/IPs in /var/named on the new server afterwards though.
Cheers
