The license of NVIZ does not seem to be free software.
From: src.contrib/GMSL/NVIZ2.2/LICENCE.txt
* NVIZ: multidimensional visualization for GRASS GIS
*
* Original program SG3d for GRASS4.1, 1993
* Bill Brown and David Gerdes
*
* GRASS4.2 Motif version: Bill Brown and Terrance McGhee
* GRASS4.2 and GRASS5.0 Tcl/Tk version:
* Bill Brown, Terry Baker, Mark Astley
*
* Copyright 1993, 1995, 1999:
* Bill Brown, Terry Baker, Mark Astley
*
* Modified by Jaro Hofierka 1999 for LINUX and Tcl/Tk 8.0
*
*/
/*
* The visualization library and programs, both binary and source is
* copyrighted, but available without fee for education, research and
* non-commercial purposes. Users may distribute the binary and source
* code to third parties provided that the copyright notice and this
* statement appears on all copies and that no charge is made for such
* copies. Any entity wishing to integrate all or part of the source
* code into a product for commercial use or resale, should contact the
* the authors of the software.
The last sentence renders it incompatible with free software (and with
GRASS therefor.) 
We need to contact the authors and politely ask them to make it free
software compatible with the GPL.
Is anybody still in contact with them?
Bernhard
--
Professional Service around Free Software (intevation.net)
The FreeGIS Project (freegis.org)
Association for a Free Informational Infrastructure (ffii.org)