Morning Musume hadn't debuted officially in 1997. Their first major single is from January 1998.
The question for me is, will Ayaya be there? With Mikity out of the picture nowadays, it looks like a no go for her. So no GAM, but what will Ayaya perform if she's there? Egao doesn't feel like a Kouhaku song to me.
Berryz and C-ute fans will have to contend with a back dancer role for their favorites I'm afraid. It is because Momusu is above Berryz and C-ute in the H!P hierarchy, especially with something as traditional as the Kouhaku Utagassen.