Gscopes can be used with meta collections but the gscopes.cfg needs to be defined on the component collections as it is applied as part of the index build.
Once the gscopes are assigned in the component collections they are immediately available in the meta collection.
Note: gscopes used across collections will be combined - so if two component collections both define the same gscope ID then this single ID will hold items from both those collections when used in the meta collection.