Friends have joined in combat against even reasonable actions before, so maybe when he's attacked back (and maybe also has good relationship with the dog)? Test it and find out, I'd say.
The happy thought they get when they sleep in their own room is dependent on room value.
That's not a simple topic, but unless they're nobles, it maxes out before it hits royal. Accessing through stairs with a hatch is little better for value than using a door in wall, though.
Smoothing/engraving is never admired. Functionally, the point of smoothing and engraving is largely to give happy thoughts to you (the player).
Buildings are admired when standing next to them, but it's not likely you're having problems with easily cheered up dwarves. Some very closed-off dwarves practically require admiring their own buildings; sticking those same buildings in hallway isn't as effective for saving them in particular.
It may be that your dwarves fight each other in taverns or the like, and thus corpses of your friends hitting the dancefloor right in front of you puts the damper on any party. Sticking them in their own room, smoothing and engraving things, has been noted as one way some people have improved their mood while keeping them away from other dwarves.