If I just make the list the same for both sexes though that runs a major risk of multiple Norns in the same run getting the same name.
To be fair, that risk is always there. I don't think it makes a statistical difference if you pull names from one large list, or from two identical large lists.
If I recall right, the standard autonamer doesn't give a flip either way if a creature already has the selected name or not. It merely relies on the sheer size of it's namelist to minimize doubles.