Sam:
The ADuM6000 is an isoPower device and as described in AN-0971 will have emissions at 180MHz on the primary side due to the tank circuit frequency, and at 360MHz on the secondary side due to the rectifying frequency of the isolated DC to DC converter. AN-0971 recommends the use of stitching capacitance for the most reduction in emissions.
It would be best to review their layout and schematics, as suggested here. Sharing these documents could be done by email privately if desired.
Regards, Brian