Nevermind, it was nscd. It apparently has a bad habit of not clearing out old DNS servers.
11/10/2009 14:41:58.128NoticeNetwork AccessUDP packet droppedx.x.1.2, 43485, X2, zimbra.domain.orgx.x.0.30, 53, X0UDP DNS (Name Service) UDP
12 (DMZ->LAN)
Above is the error, I was getting (anonymized of course). A quick run of netstat -vp --udp revealed it was nscd sending the DNS requests. Running nscd -i hosts to flush out the host cache seems to have done the trick.
Sorry about wasting your time and cluttering up the board. Thanks for the responses though!
Netstat:
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
udp 0 0 zimbra.domain.org:52561 x.x.0.30:domain ESTABLISHED 2579/nscd