Things affected by Time.timeScale are objects that rely on the deltaTime that Unity provides through Time.deltaTime. You should see Time.deltaTime referenced in SkeletonAnimation's code. That's the only place it gets affected.
If you want SkeletonAnimation to be independent of Time.deltaTime, you need to provide it an alternate means to determine deltaTime. There are several ways to do this. But it can be done with something like a GameObject with its own timer component. Or you could edit SkeletonAnimation and build this time-tracking functionality into it. This has the downside of not sharing the time calculation with other objects that may need to be timeScale independent.
You can get low-level, timeScale-independent time from UnityEngine.Time.realtimeSinceStartup. Store the time and keep track of it per Update(). Subtract current time by previous time and that will give you a delta time.
The formula is:
delta = current - previous;
This custom delta is what you'd pass to SkeletonAnimation.UpdateSkeleton INSTEAD of Time.deltaTime.
You'd do something similar if you wanted Unity Particle Systems to work independent of Time.deltaTime
(bonus tip: for particles, you need to use the Simulate(float) method.)