As a disabled Veteran the only thing I can tell you which might be a factor is that before a disabled veteran is laid off the company should look long and hard at the tax advantages it will be losing.
Given two equal employees, the disabled veteran returns at a minimum, a 10% tax advantage to the company. So, although I agree with beth as to the law, the practicality is, it would be stupid to lay off a dav BEFORE an equal non-dav employee.