It is not clear what the words "identical wallet addresses" or "ineffective" mean, nonetheless, if you have five wallets, they will each generate up to 1 million mint transactions. Even if those five wallets were created by copying a single wallet, those 5 million mint transactions will all be unique, so we have no reason to believe this would be any less effective for the purpose of mining, although it has not been well tested and is not recommended.  See:
https://bitcointalk.org/index.php?topic=1748358.msg51491559#msg51491559 (last paragraph)
https://bitcointalk.org/index.php?topic=1748358.msg51535568#msg51535568 (first paragraph)