I was wondering what took you so long to respond :^)
I did state that this might or might not be a problem. The consideration that I have is that most zappers do not have much if any filtering on the DC input and the distortions that can be generated by the stepped wave might have a negative influence on the effectiveness of the zapper due to distortion of the square wave.
I have not tested this as I have not had time but until I see otherwise, I am still skeptical of using a UPS for this purpose.
Otherwise, the UPS is a great device. I have one in my bedroom that runs my clock and a flourescent lamp so that I am never left in the dark. :^)
I also have one UPS for each of my 8 computers, including my laptops, one for my TV, VCR, DVD, and cable in the living room, one for each of the 2 portable telephone systems in my house.