I had asked the LIbera admins whether there were any other services nicks besides chanserv that would ever show up in nicklist, and they had claimed no. But I do have some 10 year old logs from a defunct network where limitserv did join the channel, and same for StatServ.
As far as a consistent detection, I'm not sure. There may be something in "/who chanserv" that's useful, but even that isn't completely consisent. The first word in the reply is 'services' at several networks, but at Rizon it's 'service' instead. There's not a consistent network block against normal people having nicks ending with 'serv'.
The only time I've been able to replicate the [#channel] notice is for the /chanserv set #channel entrymsg message goes here, since I don't even see the channel message listed for the lines listing the reply to getting the AOP list for a channel. So definitely the [#channel] should go to the channel window, and that might be an unintended consequence of my faking a nick chance against chanserv.
