This begs the question if you have summon scamp in one hand and summon Clannfear on the other, what do you get, two Daedra?, One Powerful Daedra or something Else?
If I am correct, you cant combine spells of a different name. I think in the video Todd says something along the lines of "If you put the same spell in each hand, you can combine them". I could be wrong, however.