Is not about aprove or disaprove, if you go against any license(like MAME's) the emulator is illegal, if you stole an open source project code to use in a closed one your project will be illegal(if the license of the open source one is against that of course)
If you put recent roms in MAME and distribute binaries it will be illegal
Read MAME's license:
http://www.mame.net/readme.html
VII. Derivative Works
---------------------
Derivative works are allowed, provided their source code is freely
available. However, these works are discouraged. MAME is a continuously-
-evolving project. It is in your best interests to submit your contributions
to the MAME development team, so they may be integrated into the main
distribution.
There are some specific modifications to the source code which go against
the spirit of the project. They are NOT considered a derivative work, and
distribution of executables containing them is strictly
forbidden. Such
modifications include, but are not limited to:
-
enabling games that are disabled
- changing the ROM verification commands so that they report missing games
- removing the startup information screens
If you make a derivative work, you are not allowed to call it MAME. You must
use a different name to make clear that it is a MAME derivative, not an
official distribution from the MAME team. Simply calling it MAME followed or
preceded by a punctuation mark (e.g. MAME+) is not sufficient. The name must
be clearly distinct (e.g. REMAME). The version number must also match the
number of the official MAME version from which you derived your version.
If you say your emulator is GPL and it doesn't i think(not sure) it will be illegal too
Of course if you use an illegal emulator i believe in most countries you will not be the outlaw one, who will be is the emulator author, but if you have illegal roms in almost countries you will be an outlaw