I wanted to do this JScript, but I had to do it in Python first, to establish that it was actually possible (with JScript, you’ve got to mess around with VBarrays and such).

# Using one of the CrowdFX sample scenes:
Application.SelectObj("Pedestrian_Mesh.Actor_Copies", None, None);
o = Application.Selection(0)

a = o.ActivePrimitive.Geometry.GetICEAttributeFromName("Materials")
print len(a.DataArray2D)
print len(a.DataArray2D[0] )
print a.DataArray2D[0][0]
for s in a.DataArray2D[0][0]:
    print s

# 1
# 1
# (u'', u'Sources.Materials.PedestrianLib.Shoes', u'Sources.Materials.PedestrianLib.Hair', u'Sources.Materials.PedestrianLib.Legs', u'Sources.Materials.PedestrianLib.Skin', u'Sources.Materials.PedestrianLib.Shirt')
# Sources.Materials.PedestrianLib.Shoes
# Sources.Materials.PedestrianLib.Hair
# Sources.Materials.PedestrianLib.Legs
# Sources.Materials.PedestrianLib.Skin
# Sources.Materials.PedestrianLib.Shirt

After I had it working in Python, I was able to figure it out in JScript:

// Using one of the CrowdFX sample scenes:
SelectObj("Pedestrian_Mesh.Actor_Copies", null, null);
o = Selection(0);

a = o.ActivePrimitive.Geometry.GetICEAttributeFromName("Materials");

x = new VBArray( a.DataArray2D ).toArray();
y = new VBArray( x[0] ).toArray();
for ( var i = 0; i < y.length; i++ )
{
    LogMessage( y[i] );
}