As long as they are washed well (ideally no trace of fixer left) you're good to go. I'm going to continue doing this with scraps as well, I still have the Valca roll and countless feet of 16mm film that "spaghetti-ed" in my Canon Scopic- a pinhole camera is now in the making. While not an ideal stock, I like the whole recycling aspect of doing this. Some craft-makers make beautiful jewelry from stay-tabs from aluminum cans, no doubt the same can apply for a photographer using recycled scraps of film/paper to make a unique photograph.