I've done it either way and you will be prompted to merge during import if necessary. Not just name, but if the two users (whether admin or not) share an email address there will also be a user merge prompt.
My preference is to have contol afterwards so on the next import I will use a different admin name/email and do any merging/deleting of accounts afterwards.
You have control outside of the (admin cp) of superadmin status by using the library/config.php and defining the user ID of the super administrator there: