hi ronslow
Some years ago I tested seamless with importing HAnim avatars that were created using Vivity studio. Here is the tutorial that was written to show how to do this.
http://www.seamless3d.com/tut/import_hanim/
Because this was written a number of years ago and most of my focus since has been on making seamless be able to do nurbs modelling, lots of big changes have been made to seamless since then so I can not be sure what exactly works now and because I don't know of anyone who seriously uses H-Anim, I don't have a lot of enthusiasm for the subject these days.
Seamless can’t import XML code but it can import X3D encoded with classic VRML but you will have more chance importing H-Anim with VRML97 code as there are a few simple minor things that X3D VRML classic encoding can have that seamless may not have been made to deal with.
There is no specific command in the menu for importing HAnim, You open the VRML/X3D file as you would a smls file and then right click on the HAnimHumanoid node in the scene tree and select convertToSeamless as shown in the tutorial.