Well if LR states that multiple account s are allowed then where is the question of same IP. Be it same IP or not one PERSON is allowed to have muliple accounts so even if the IP is same it won't matter.
Well, you can see the option of ip security in the "settings" tab. Actually this option plays a role only when you access from different country or something. LR will assume someone is hacking your account, and won't allow to login provided you enabled the security option.