I'm not sure that will work. From past testing with gvgw, I found that if 2 clients are set to the same X_XMPPPriority value, then the last one to log in will receive the call. In my case, client A is asterisk, client B is a softphone which uses/used gvgw when the pbx is unavailable (down, updating, etc). I had Bill change the setting on my account to a lower value than 127 (100), which achieved the desired result. PBX would always ring unless actually down. Then calls would automatically forward to simonics gw.
I think the OP might be better off with a master/slave setting maybe?
I suppose before doing anything out of the ordinary, the OP should just setting both obi's for the same account to see what the result is.
It works with OBi2xx devices and OBi phones connected directly to GV. it did not work with OBi1x0 devices but that is now moot.