Can you blank out an ABS light by disconnecting the battery or must it be cleared by a scanner?

No. As long as there exists a legitimate mechanical problem that ABS light will stay on regardless until you fix the problem. A scanner will get you pointed in the right direction and after repair you can clear any fault codes. I feel your pain. I replaced both front hubs and the right front has a defective ABS sensor, which means I get the joy of tearing that apart again.