I don't "think" I would use them for an OIL cooler. Trans fluid needs to be kept warm as much as cooled down. That's why it goes through the radiator, warmed in winter, cooled in summer.
Engine oil can benefit from cooling and the extra oil capacity of an external cooler.
Last time I replaced a radiator I also worried about those two 'open' lines. Cap them to keep the mud out if you like, remember they keep the trans fluid separate from the coolant. No A.T., no use.