Spine-Unity is made up of actual Spine-Unity and Spine-C#.
v3 needs a new Spine-C# but Spine-Unity will stay mostly unchanged.
v3 is mostly changes in how transform information travels through the bone hierarchy, which is defined in Spine-C#. Spine-Unity's core is mostly asset management and rendering and won't noticeably change.
Spine-Unity's utility classes, where it interacts with bones, will likely break though in cases where scale is not (1,1) or was negative or where flipping was used.
Because of this, the extra tools Mitch made may need to be fixed but he did say it would be easier supporting v3 than it was supporting v2.
Can't comment on Gunman and Hitman compatibility 'cause I don't know.
But if you want to make new animations, they'll work fine in all cases where you didn't change the scale to anything except 1,1 and you didn't use single-bone IK (which was broken).
It's really the utility scripts that need updating.
