Смотрим первоисточник (F1):
Note: The File Link Manager is not included in 3ds max 6. If you open a Autodesk VIZ file, you cannot Reload or Bind geometry from the original DWG file.
Что касается filelink.dlu, то, насколько я понимаю, он служит как раз для совместимости с VIZ4:
Any AEC object (walls, doors, windows, etc.) in an Autodesk VIZ file is automatically converted to an editable mesh object when opened in 3ds max. Autodesk VIZ models may also contain File Link created objects that appear as VIZBlocks or Linked Geometry.
File Linked VIZBlocks in 3ds max:
A VIZBlock is a compound object similar to a nested AutoCAD or Architectural Desktop block. If a drawing containing nested blocks is file linked to Autodesk VIZ, the block objects display in the Modify panel as VIZBlocks.
3ds max recognizes VIZBlocks when you open a MAX file created in Autodesk VIZ. You can access the sub-object hierarchy, rename sub-object components and even extract sub-objects of the VIZBlock. You are also allowed to add modifiers on top of the sub-objects. You cannot attach objects to a VIZBlock as you could in Autodesk VIZ.