I've had basically the same problem. I made a little progress today. I'm past the "Can't Detect Device" issue. I can't get the serial GW to enter inclusion mode via the Vera UI, but then again, I can't get it to do it with an Ethernet GW either. So, it's not working yet, but I did get past the Can't Detect Device problem.
Since the UI7 files don't work for me at all (Create Device doesn't appear to do anything when I use the UI7 files). I deleted all the *Arduino* files from /etc/cmh_ludl folder, then I uploaded a fresh copy of the UI5 files. Then, before I created a device, I replace just one file, the L_Arduino.lua file, with the UI7 version.
Now when I create a GW device, it creates successfully, and I don't get "Can't Detect Device". The plug-in doesn't actually work. I can't start inclusion mode from the plugin, but as I said, I can't do it on an Ethernet GW either. From the Ethernet gateway, I can, however push the physical button on the GW and it shows that I did so in the Vera UI. I didn't (yet) hook up a physical button to the Serial GW to initiate inclusion mode, but I'll try to do that tomorrow and test to see if I at least have parity.
At a minimum, I'm glad to be past the Can't Detect Device.
Does anyone else have a serial GW fully working on a Vera Edge, with UI7, using the UI7 branch?