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.