I thought overlay approaches were using GPS guidance to follow an NDB or VOR approach track by using the GPS nav line, not using the waypoint bearing pointer on the RMI as you would use the ADF needle as has been suggested here.
Any overlay approaches I know of use a GPS generated track and don't use the waypoint bearing pointer. These approaches benefit from the tracking accuracy which comes with the scaling of the CDI. This accuracy is not possible by just using a bearing pointer.
Perhaps there is more than one style of overlay approach. Using the bearing pointer seems a reasonable option for an NDB approach. The pointer would be nice and steady, there would be no coastal refraction etc.