Just happened to be doing a bit of research into 10E's and ER's. If you can view the two photos of the mortising attachment - yes they do look the same.
Photo # 1 (from page 15 of the 10ER manual - courtesy of Song of the Great Lakes site)
http://www.songofthegreatlakes.com/pics/ssman/ss10er15.jpg
You'll have to enlarge this photo to 200%
Photo #2 (from the Shopsmith on line catalog - Again an enlargement is helpful.
http://www.shopsmith.com/ownersite/catalog/rm_hollowchisel.htm