Ooh I forgot all about those! That is such a simple yet creative application for them... I wish I thought of it!
This online merchant is suggesting to use them as aquarium decor, so I guess it's ok to use them as dividers.
I hope you post pics of your dividers if you go through with this.
I bet you might be able to sell these dividers on ebay too.
There's definitely a shortage of aquarium dividers - particularly opaque, aesthetically pleasing ones. All the dividers on ebay and everywhere else are clear...that is next to useless for betta tanks.