Here is the situation
I currently have our "real" domain ccmcks.org hosted on Lunar pages and name servers point to Lunarpages even though the domain registrar is someone else.  I have recently added a new domain ccmcks.com that is registered by Lunarpages and also uses Lunarpages name servers.

I have entered ccmcks.com as a "parked domain" on cPanel. And this works to redirect ccmcks.com to ccmcks.org.

All our e-mail is hosted by lunarpages under ccmcks.org

We will be implementing an in-house exchange server soon.  I would like to use the ccmcks.com domain name to test the exchange server before we go live and have mail for ccmcks.org routed to our new exchange server.

Will it work to just set the MX entry for ccmcks.com to the public ip address of the new exchange server?
My concern is that the MX maintenance screen on cPanel says to use a fully qualified domain name for the MX entry.  Does an ip address count as a FQDN in cPanel?