wcnngt,
Check your Phone Port OutboundCallRoute. I guess when you set up 911 on Callcentric, then the OBI placed a {(911):sp2} rule there instead of the default sending out to li. In this case your trunk group does not come into play as it consists of li,sp1.
I have a very similar set up to you, using the Xlink to link mobiles into the line port. After discovering the "toggle battery" option I set up the same tg as you:
Voice Services -> Gateways and Trunk Groups -> Trunk Group1 -> TrunkList -> li,sp1
Here the emegency numbers are 999 & 112. Now in my Phone Port OutboundCallRoute I have a rule ...,{(999|112):tg1},...
This means that 999 will go out to line and my mobile phones first. If both mobiles are out of the house (but someone is still at home!) then 999 will go to sp1 which is
Sipgate.co.uk, which is also set up for 999.
This means a trunk group can give you a back up to your normal emegency service, but it needs to be set up with care.
I believe RonR has a post here somewhere that shows a 911 with two backup routes using a trunk group.