You don't need to flatten the metal teeth on blind nuts, but they're rarely cooperative and frequently break off on their own unless you're able to remove the part that's getting a blind nut to hammer it in from the back. I prefer gorilla glue for holding them in place. a super thin coating around the edges will foam up a bit to adhere between metal and glue along with filling in any gap between the two in the hole. Just have to be careful not to let any glue get into the threads.