If you are salaried, I can see how that might be true. If you are on incentive for productivity, you would have to expect the productivity to be calculated at zero, and any compensation based on productivity also zero (if you had stayed home but done no production, same effect.) Also, I suspect any compensation provided by the government could be deducted from any base salary--no double dipping. More to the point, while some colleagues may sympathize, others might see your reserve affiliation as a voluntary conflict of interest, unless your reserve obligation arose from an agreement you made before hire and they were aware of that obligation and of the possibilities of your being called up.
No one will like being threatened with action under USERRA.