Randy, hope you're still a readin',
So, I preped some of the supplement last night using the MgCl2 from the new bags. I diluted the stuff out (necessary to run on this instrument) and ran it on an analytical instrument here at work and the ammonia level came out pretty close to the lower limit of detection of the instrument. After a quick calculation I come up with about 60 ppm ammonia (NH3) maximum in the concentrated supplement. If we were to use the supplement as I outlined above to increase a tank about 100 ppm Mg per day then you would be adding a maximum of 0.15 ppm NH3 to your tanks water with each dose. In a functional reef tank this is not a level I would be particularly concerned about. I would imagine this would be processed by the nitrifying bacteria in your tank within a few hours at most.
So, I think we are fine on the ammonia question.
One thing to note, for the supplement I preped I used lab grade magnesium sulfate (along with the magnesium chloride bags we received) rather than Epsom salts as I didn't want any ammonia in the Epsom salts to confound the results. I don't think that there is likely to be a lot of ammonia in Epsom salts since it is USP grade, but YMMV (your mileage may vary)!