First off, I've just released a port of my Iris Z-Wave Repeater driver. Give that a shot as that will tell you if the devices are able to communicate.
I do not believe Hubitat supports network wide inclusion (NWI) so I'm not surprised that battery powered devices do not pair through them. Any device that requires secure inclusion has to be in direct range of the hub.
I will say from experience that the radios in these plugs aren't super strong. Now that I have 3-6 in every room I don't notice that anymore.
