No... not for most of them. They use gouache 
paint to paint backgrounds, because it is opaque 
(when watercolor is transparent). If you are just 
painting a background for framing or for 
scanning, watercolors should be fine. Yet for 
filming (and other photographed uses) gouache 
works best. One last note: It's MUCH easier to 
paint hard/straight lines with gouache than it is 
watercolor. ;)

~Tara