The roguelike bits are mainly client-side; there are people using Evennia to develop roguelikes (not sure if any are actually released, but it can be done).
Yep. So long as you separate concerns well it’s quite doable. The heavy lifting is deciding how to turn roguelike tiles into MUD rooms, or vice versa. There were some MUDs doing procedural content back in the ‘90s, and others that had a minimap, so there’s plenty of demonstrable overlap.
On another tangent, I wish I had known Common Lisp back when I cared about MUD implementation enough to actually pour a few hundred hours into it. Of course you'd face the problem of the extension language, at least in the naïve implementation, being entirely too powerful. Still, it could potentially make it easy to script truly interesting custom object behaviors.
If I were to make a pass at it now, I'd try to structure the game system in such a way that it could power a roguelike or a MUD, since roguelikes have considerably more legs these days.