Is it possible to download the server.cfg to client from a gmod server?
Is it possible to download the server.cfg from gmod servers to the client?

I don't think that the server.cfg is sent to clients so...no but I may be wrong.
There was an exploit a few years back that did this. No longer works, so I don't believe it is currently possible.
you used to be able to do sv_downloadaurl into console and type that url into your internet browser, and there is the server files in it but you will only find a server.cfg if the owner is really stupid...