As you know, MAMEdev decided to relicense all the code under FOSS licenses. What that post meant is any code added to MAME from now on cannot use the old MAME license as it was not FOSS or GPL compatible.
Regarding VGMPlay, we're not a deriative of MAME but we do use MAME code, which used to be under the MAME license. A few months ago the FM cores were relicensed under the GPL version 2. At that point, all the MAME code we have in VGMPlay became either BSD or GPLv2 licensed.
Ootake prohibits commercial use, but could be disabled for a GPL-compliant release as the MAME core can be used as an alternative, while the MEKA code we use is in either public domain or
public copyright..
dac_control.c prohibits non-VGM and commercial use, making it incompatible with the GPL. I don't think ValleyBell would mind removing those conditions though...
The only license violation we have right now would be the PortTalk code (which prohibits any distribution of source code). It can be safely removed if you don't need the hardware support.
With those steps done VGMPlay could be redistributed legally under the GPLv2 and be used in GPLv2 software without any legal problems...