I understand that you want to know if the Slingbox PRO will work with the SlingPlayer for iPad if you use the HD Connect cable.
Unfortunately, it will not work. Keep in mind that the HD Connect cable will allow you to connect your Slingbox and stream the HD signal on High Quality (not High Definition quality) using the Component cables.
The following link will provide you with the related chart and information.
Finally, the Slingbox SOLO and the Slingbox PRO-HD are the only Slingbox models capable to stream the iPad's higher resolution. Make sure to check the following link in order to get further details about the SlingPlayer for iPad.