I have looked into Undying code. It uses completely different animation system, placed into dwi.dll. SkelMesh is a simple wrapper around DreamWorksInteractive skeletal animation system. Even math functions are taken from this library. It's too complex to reverse this. And there is no real reason to do this: there are no user-made models for Undying. Possibly, I will later look deeper into code, but I cannot promise anything.
I have decided to support at least something from Undying. Textures are now supported.