Why don't you test it?
I suspect if you have role A on child course 1, and role B on child course 2, and if both roles A and B are included in the list of synchronized roles, then you should end up having both roles A and B in the metacourse - but I don't know for sure.
--sam
Ok - I just did this (Work avoidance strategy...) Tried on 1.9 but I daresay it will be the same in 2.0 - it's what Sam says - the user now has both roles in the metacourse.
It would be easy to do this, but I suspect it is not a good idea. I have tended to avoid putting users into the parent course, only the child. What has concerned me is a possible conflict in a backup/restore that could wipe out the Role in the child course, not recognise the Role in the parent course and leave the course without anyone in a Teacher Role. Never been [foolhardy.. erm... brave... yes that is it] brave enough to find out either...
I doubt Moodle is quite that flexible. Give it a try, certainly, but I would not hold out a lot of hope. Given I said that, if it works then then I would be happy to be proven mistaken here. Cheers...