They more I see of SMAP with either Yamashita Tomohisa or Kis-My-Ft2 the more I realize that the interactions between senpai-kohai for them is a true mentor-mentoree one. SMAP has in the past been more removed from other groups so you did not get much in the way of interaction between them and other groups. But with this recent shift with them working with Yamapi and Kisumai this has been changing, or at least with these Johnny's.
I feel that the interactions with SMAP for Yamapi and Kisumai will benefit them more than just simply trying to ride on their coattails. SMAP are tried and true veteran idols and the first to make that successful switch from just being idols to all around entertainers. Yamapi and Kisumai are getting the chances to work side by side with them, giving them valuable opportunities to learn from the pros as it were.
And I do think SMAP gets something out of this relationship as well. At this point of their careers they have hit so many highs it is probably hard to figure out what the next goal is, and by having younger talent to mentor it can give them that new goal, to nurture the ones that are coming up after them. And they seem to love interacting with the other Johnny's, even though they have not gotten many chances because of how busy they are.
I can understand why some fans may feel begrudged to Yamapi and Kisumai for getting these chances when really no other Johnny's act has gotten to. But timing is everything and they just got to be the lucky ones that where placed under Iijima Michi's management when it seems things are getting serious about finding the next president of Johnny's & Associates.
So in the end I see this as a clear win-win situation, with the younger ones getting to learn from those that can be considered masters of their trade, and with SMAP gaining a new way to find job satisfaction by helping their kohai rise in the entertainment world.