HI James. I wouldn't particularly see a problem with this. MCU can be added as conferencing MCU in CUCM then added to Media Resource Group, and folks can escalate calls to the MCU. You then can have H323 registered to VCS if you need to. SIP may be a bit different, but the MCU doesn't register SIP directly to CUCM, so it seems feasible. What would be a concern is dialing out SIP from MCU, as it may redirect the request towards the VCS versus the CUCM when placing the call out, so would be wise to have SIP disabled, and place the calls natively.
Be watchful though, if using TMS and booking meetings etc, you have to mindful of the port count, and that you don't over book the MCU with folks creating conferences on the CUCM side also.
Telepresense Forums would be best to plant these questions if you can. Some good posts here:
https://supportforums.cisco.com/thread/2167295
https://supportforums.cisco.com/message/3715176
http://www.cisco.com/en/US/docs/telepresence/infrastructure/mcu/install_guide/Cisco_TelePresence_MCU_Deployment_guide_1-31.pdf
Hope this helps.
VR
Patrick
