If you are looking in nameserv you're asking in the wrong place.. we only have a nickserv...
And preventing the use of characters or a string in a nick would be an IRCd function, not an anope one.. most ircd's have ban nick blocks or QLINE blocks in their conf.. if you do want to use anope, there is the OperServ SQLINE command which just exposes the ircd's functionality through anope...
Note though that none of those will allow exemptions for channel ops... that completely illogical given that channel access is something entirely different from server/network access and which nick a user has does not vary from channel to channel thus is linked to the server, not to the channel.. First problem for exempting ops would be "ops on which channel..
".
The best you can do to prevent someone from using [GM] in their nick on a given channel would be to ban *[GM]* and give ops exempts, invitations or have them use chanserv invite.
In any case banning nicks globally cannot be done based on channel access.. you can SQLINE *[GM]* but that would affect all users - except opers maybe..
