Most wings have some sort of dihedral built into them. Generally speaking the less the dihedral the better the plane will fly (I should say cleaner not necessarily better) BUT it wont have the self correcting characteristics that dihedral provides. I normally dont put as much dihedral in a wing that is called for - but I wouldnt try to remove it from a wing or build a new wing because of it either. I just finished an 8ft Beaver that I will put floats on next summer. The kit calls for alot of dihedral and most Beavers get put on floats at some time or another. I only put about 1/2 the dihedral that they called for but they wouldnt tell you to put that much if it had an adverse effect on float flying. Also, any plane will flip if there is enough wind - you will just have to pay more attention when windy.
Hope this helps you - where did you read that it is bad for floats? I am interested in reading why.
tks1