More than likely your block will not be cracked from simple coolant freezing, Dingman is correct if it was cracked the oil will be a grayish colour, hmmm, it may be brownish if it was pure water in the system.... either way it will be easy to tell. A couple of things to watch for though, cracked fins on your rad, a colapsed hose, and make sure that the frost plug is still seated. I would recomend bringing it indoors and letting it thaw out, top it off with regular water and let the jeep run until it warms up now check that the oil is still just oil, and check the rad hose, remember to check the return hose as well they should be firm and hard to squeeze if the system is flowing water properly, finally check for leaks. If it all checks out refill it with coolant.
Good Luck!