Are there any secrets in Sonic Adventure 2 Battle

last story (finish both hero and dark stories)
kart racing modes (finish kart levels)
secret karts for each character (finish all their missions with any rank)
secret skin for each character- multiplayer (finish all their missions with A rank)
Green hill zone (get all 180 emblems)
boss fight mode (finish all three stories)
Secretary theme (go to the menu theme select screen then rotate the control stick clockwise for as long as it takes then there is a chime and there's a lady who appeared in 5 seconds of the game [ shes the presidents secretary ])

so to answer your question

yes, yes there is.