you need to reset the VG200 in order for the new configuration you just created to be downloaded to the VG200 via MGCP.
when you're in ccmAdmin and you configure an MGCP endpoint and press the 'update' button, the VG200 has no idea you did this change.
you must tell the VG200 to download its configuration from callManager. this can be done by rebooting the VG200, pressing the 'restart' button from the ccmAdmin gateway configuration page or using the 'no mgcp/mgcp' commands in global mode on the VG200.
as far as MGCP interaction with ccm and the VG200 here's a quick overview:
MGCP is a master/slave protocol.
when you configure an MGCP endpoint in ccmAdmin, you must also configure MGCP at the endpoint. in this case your VG200.
you must provide at least three commands to the VG200 for MGCP to operate correctly with CCM:
1) enabling mgcp - this is to enable the protocol for use on the device.
ie: vg200(config)# mgcp
2) tell mgcp its call agent - this is the device that controls the MGCP endpoints operation. (this would be your call manager)
ie: VG200(config)# mgcp call-agent 10.10.10.10 2427 service-type mgcp version 0.1
3) tell mgcp that the call agent is ccm - this is the device that provides the MGCP endpoints configuration. (this is usually your CCM TFTP server)
ie: VG200(config)# ccm-manager mgcp
there are a few more mgcp options not mentioned here.
see these links for more mgcp info:
http://www.cisco.com/en/US/tech/tk652/tk701/tk419/tsd_technology_support_sub-protocol_home.html
http://www.cisco.com/en/US/tech/tk1077/technologies_tech_note09186a00801da84e.shtml