You will end up with issues of having the same UID used twice, rather than duplication. Also objects on ADT borders will be missing collision on one of them. In the end, just have someone save all tiles once a week or so and stuff will be fine again.
To avoid UID-duplication, you can have a non-synced 63_63 ADT in the folder with a different (large) UID per designer. That way, Noggit will use that one as smallest rather than the same for everyone.