Unfortunately we don't know the intrinsics of this Animancer package (it's funny to see that someone re-created the old Unity 3 legacy animation system on top of Mecanim however :nerd: ).
If Animancer is based on a normal Mecanim Controller asset and triggers transitions between states of the Mecanim state machine accordingly, it could theoretically be used with the SkeletonMecanim component. It would make no sense to use it though, as you are putting two limiting wrappers on top of the Spine API: from directly setting animations, to the Mecanim state machine, to directly setting animations again.
So in short: it might be possible, but it does not make sense and potentially causes a lot of problems.
