If the 1/2" thick boards are cupped badly, they may not be of much use. The pressure rollers on a thickness planer will squash the cupping in front of the cutters, so you'd end up with thinner boards that are still cupped when they come out the back side.
Sometimes, ripping and crosscutting warped boards can produce useful (smaller, of course) pieces. But, ripping cupped or otherwise warped boards can be dangerous, even if your table saw has a riving knife.
If the reclaimed wood has weathered nicely, you might consider cutting it into shorter pieces, and attaching them to the front of the bar in a butcher-block style layout on top of a plywood underlayment. I'd use good, straight stock for the top, however. You'll want the top to remain flat and smooth.