This looks promising but I'd like to delve a little deeper. My intended setup is to have 2 ReadyNAS units and one Linux server on a single subnet with an APC or Tripp-Lite UPS. Can one of the ReadyNAS units be set up to receive its UPS signals from the other, or from the server if that is easier?
If you get one NAS to share the UPS, when you go to the other NAS and browse to System > Power > UPS in Frontview you should be able to use the "Enable monitoring of UPS physically attached to a remote ReadyNAS" option. You would check this option, enter the I.P. address of the NAS the UPS is connected to via USB and click apply.
Note of course the power supplies of both NAS units, your PC and your router/switch need to be connected to a UPS for this to work.