Interface speeds reported in the interface tab in the UMP USM Portlet are the ifSpeed values returned by the monitored device. If they are incorrect, you can override them in the snmpcollector probe so that the correct speed is used to calculate metrics based on the overridden ifSpeed, but this value will not appear on the interface tab by design.
To see any overridden ifSpeed values on the interface tab of the UMP USM Portlet would require an enhancement request.