Delta mush isn't a smooth di per se', it's a binding state trick.
You smooth a mesh and save the delta of points from full detail to smooth in the bind pose, you then deform and smooth out the full mesh, and lastly re-apply the deltas back on the deformed smooth mesh to reinstate the high frequency detail and irregularities.
A basic implementation like that is quite simple actually, and that's why it's kinda brilliant.
It's pretty easy to do with OOTB XSI actually if you use ICE to apply shapes after the envelope, or use ICE to skin things in the modelling stack.
Take mesh, smooth it, shape animate from smooth to HR with shapes set to local (it will use the local reference frame of each point).
Then apply your skinning, and apply a smooth deformer on top. Lastly apply the local shape through ICE to recomputed point framesets.
The reference frameset is trivial, Y is the normal, X or Z is the first edge projected on the normal's plane, the last axis is the cross product of the two.
You also have ICE facilities for that, I believe, and if they match the same system used by local shapes they should just work.
If you instead do the skinning in ICE in the modelling stack, then you have even less work to do, as you can use local shapes OOTB (they are meant to preserve local transforms in shape with something live going on in the modelling stack).