IMHO, yes, these are protected benefits. Basically, any optional form of benefit is protected unless there is a specific exemption, and as far as I can recall, no such exception exists for these.
As a purely personal editorial opinion, I can't imagine why an employer would want to take away such an option for someone who is engaging in qualified military service, but of course I don't know the specific situation. My general philosophy is to make things as easy for these folks as possible.