Chances are good that even if they're not eaten, your turtle will rip them up just for something to do.
I've tried cabomba, and my RES wasn't impressed with its edibility (not sure if this is a word, but you know what I mean

), but it did eventually fall/get ripped apart.
For me, the best thing to do has been to decorate with fake/plastic plants (a turtle may take initial nips at them, but will quickly realize they're not for eating) and add aquatic plants that I know will be eaten, like anacharis, duckweed, water hyacinth, etc.
"You become responsible, forever, for what you have tamed." -Antoine de Saint Exupery-