No, the autopilot on the 737 cannot be engaged on the ground. If you press the button, the autopilot does not engage, so there is no disengagement, at least in the way that you've worded your post. If memory serves you'll still get the red A/P flashing light, but no horn. Mind you, I haven't tried this since my initial sim when the instructor was trying to prove that it can't be done, so my memory of what happens may be clouded by time.