Hi Geert,
If you want transcoding to be done on MeetingPlace, you would need to enable High Quality in System Configuration > Media Resource Configuration. This will of course cut the resource pool significantly.
If you use High Capacity mode, then MP can negotiate only G711 and if the calls are coming from CUCM to MP with a codec other than G711, the call will drop.
MeetingPlace doesn't really care if you have MTP enabled on CUCM as long as you have enough resources on CUCM to support terminating every call coming to MP on CUCM.
-Dejan