Hi Nick.
It depends on your selection during master data upload, if you select a hierarchy in the hierarchy selection tab then any other members not part of the hierarchy will not be loaded, so in your case non-existent.
so it all depends what do you want to archive, do you want to load all member from that info object? then just leave hierarchy empty during the selection.
If you want all members outside a hierarchy into a custom one in BPC then you have to use routine BADI. or you update the hierarchy in BW.
Andy