Yeah, the company I work for actually has a public Discord server for providing support (and hosting our "community" - with some exclusions due to privacy concerns).
Because of that all of our internal staff discussions takes place in Discord, in channels that can only be seen by the "Staff" role (though modded Discord clients can show these channels' names - because channel listing, both voice and text based, seems to have been relegated to client-side so the server just sends ALL channel names, but not the actual contents unless you have the role since that is checked server-side).
While we do have a system that management based staff are invited to (I won't name it because NDA, but it's incredibly easy to guess), but it is only used in case there's a *massive* Discord outage and the staff end up in an extended communications "blackout" because of the outage - however it has _never_ actually been used, at least in the time I've been part of it.
Yes, most of my work conversations happen on discord servers. Discord provides a better chat service than slack, so I don't see how it would be unusual for people to use Discord over slack.
