Are bullets with polymer tips legal to use for big game hunting?

The answer depends on which weapon you are using.  If you are hunting during an any weapon hunt using a high powered rifle (7mm) a bullet with a polymer tip is legal to use for big game hunting.  If you are hunting during a muzzleloader only season you are required to use a patched round ball or conical non-jacketed projectile comprise wholly of lead or lead alloy, so the polymer tip would not be lawful to use for hunting big game.