Thanks for the reply joecaption!
I was really only questioning whether or not to tape the short 4" butt joint in the center of the picture. As for the metal corners, not looking to tape over them, was just trying to make sure joint compound (#90) was the proper mud for that application.
The area pictured is actually the wall dividing the stairs on a split level. It sees absolutely no abuse from traffic but did see it's share of crack inducing stress due to a sinking foundation at one corner of the house. This has since been remedied via six helical piers thus I can finally perform permanent repairs.