The only documentation for the ActiveX vla-* functions is written for VBA and is located under the 'ActiveX and VBA Reference' section in the VLIDE Help Documentation. The associated help file is the 'acadauto.chm' file.
Unfortunately, when the help migrated to the online content in AutoCAD 2011, the ActiveX / VBA reference was removed. IMO, a ridiculous decision, since new developers looking to learn Visual LISP without access to the AutoCAD 2010 Help files have no reference.