When I was at an ALPA carrier, I was offered an AGR Tour with NGB. I asked the question of ALPA if I had USERRA protection, since the orders stated, "You are ordered to active duty with the permission of your governor and your permission." The ALPA Legal opinion was, "No."
I stopped by JAG on my way home from Drill one day, and asked for their opinion. The civilian JAG attorney (retired O6) told me that, in no uncertain terms, orders are orders. He told me that I have full protection.
There is no reason why this would not be covered. If you were never in the service, and one day signed up on a whim, you would have the same protections with your employer. I recommend that you make an appointment to speak with JAG. Getting legal advice from a bunch of pilots may be dangerous.
Additionally, keep in mind that the five year protection is automatically extended by any Presidential Call-Up named operation (i.e., Operation Noble Eagle, Operation Enduring Freedom, Operation Iraqi Freedom, etc.). There is no time limit on these.
I spoke with JAG during my last stint on AD. The attorney explained that the intent of the law is to make you whole, and treat you as if you had never left.
If you run into any push-back from your employer, please PM me. There is nothing I love more than making these bastards pay for their abuse of veterans.