When it runs Linux and some other tools under GPL or similar license, the vendor has to disclose the sources of the GPL parts. Ask them, if they don't comply take legal steps if possible. Maybe if you are lucky you get more than the minimum they need to disclose, and with this some useful information.
This is the great thing about GPL-licenses: Anyone who uses software based on that has no right to keep that software in secret. Even if they start out from GPLed software and modify it -- according to GPL, the modified software also has to follow the GPL. (It does apply only to pieces software using (modified) GPL source code by themselves; it does not apply to proprietary scripts or binaries running besides GPL code and interacting with each other)
What they can do is write completely new software that just speaks with GPLed software -- in that case they only need to disclose the GPLed part.
Regards!