Hi Chris,
The concerned functionality for region is not available in SAP GTS 8.0 but in that case you can develop it in a customized way at your end.
Regarding advantage of the same logical system group, there are always pros and cons associated with an approach. As I already pointed out it depends on the difference of Data Environment between the two systems and if the data is unique between the two systems, then using the same logical system group is good as it helps in minimizing further associated data and organizational structure maintenance. But if there are records that exists in both the feeder systems , then while using the above approach ,please make sure that they are in sync before the data is passed to GTS.
Using a separate Logical system group in case of any issue's/confusion will be the safe way around but will further involve efforts in configuration maintenance.
Hope the things are more clear now.
Regards,
Aman