Trial and error. Create a graphic event as long as the credit roll event, place the start of the graphic off screen at the start, and using either track motion or pan/crop, keyframe it to finish at the end of the event that is the same length as the credit roll. Should follow speed of the credit roll. You may need to change the keyframe personality/attributes from smooth to linear, fast/slow, or other speed to make it behave at the same velocity as the credit roll.
If you only want the graphic to roll at the same speed as a SECTION of the credit roll, define the section as a region, and use that as the template for the time/length of the graphic roll.
You could put the text on one track and the graphic on the other. Do the credit roll using track motion, instead of the credit roll plugin. Copy the track motion settings from the credit roll track to the graphic track. Move the graphic left/right along the track to time where it will enter the scene.