Hi,
Can you help us understand the exact setup? Do you have two sites A & B with A having phones registered with CME and site B has phone has phones registered with CUCM? Also is the same CME router added as an h323 gateway on CUCM?
Is the Call flow below correct?
IP Phone (Site A) >>>> CME >>>>> H323 >>> CUCM >>>> IP phone (Site B)
You can go through the below document to understand the dial-peers as it contains lot of configuration examples:
http://www.cisco.com/c/en/us/td/docs/ios/voice/dialpeer/configuration/guide/12_4t/vd_12_4t_book/vd_dp_cfg_examp.pdf
Aseem