What is the end point on the other side? Is it a gateway? You can check what digits are being sent from that far end side instead of checking on CUCM. Gatekeeper would not modify the digits you're sending to CUCM, it would simply tell the end point to intiniate signaling with the CUCM and provide it's details.
Alternately, you could pull CUCM traces and see what digits were received, which will be a more time consuming process.
HTH.
Regards,
Harmit.