yes, i use irssi to hold persistent sessions for all the twitch chats im in. doesn't require anything special beyond an oauth token sent as the server password
You could back in the early days (I did it), not sure today.
You still can, it's very useful for bots and game integrations because you just need an IRC lib in your language of choice. However, the servers aren't IRC anymore, they just have a compat shim that speaks IRC for those purposes.