It would be courteous to talk to your RCMO first. Ask the question and then mention you would be quite happy to talk direct to your desk officer if that would be helpful. In the same vein, tell the desk officer that you have spoken to the RCMO but he was not able to help you and recommended that you talk direct.
At the end of it all, advise the RCMO of the outcome of your conversation. If the topic is important, keep a note of what was said, by whom and when, preferably as the conversation is underway, not 3 weeks later.