The best method for handling access to a bot would be to use the User List. Set the users (and all possible IP/DNS combinations that you expect them to have) up in the User List under a number such as 1000. Then, use 1000 in your on texts...
on 1000:text:*:#: {
do stuff
}
Most people these days are on high speed internet, so even if they don't have static IP addresses, they usually won't change IP very often. Your only real issue with doing it this way would be if they are dial-up users. In that case, I would just set up a login to the bot and if they log in properly, it will automatically add their new IP info to the user list (/auser).
The danger with doing just nicks for bot access is that as soon as someone realizes that they only need to have a specific nick to use the bot, they will change their nick to one of the required nicks when that person is not in the channel and wreak havok on your bot.