Hey DS, I've been having similar issues to BlueSpud. It seems Steam has started including a dedicated.dylib with the client Gmod install again in a recent update, and when run with this version of dedicated.dylib (1,459,504 bytes), it gives this output:
Simon$ /Applications/Garry\'s\ Mod\ Server ; exit;
Auto detecting CPU
Using OSX binary.
Server will auto-restart if there is a crash.
Failed to find symbols for dedicated.dylib
Add "-debug" to the ./srcds_run command line to generate a debug.log to help with solving this problem
Tue 16 Sep 2014 10

6:25 EST: Server restart in 10 seconds
When run with the dedicated.dylib that you included in your GMOD archive (245,060 bytes), it gives this error message:
Simon$ /Applications/Garry\'s\ Mod\ Server ; exit;
Auto detecting CPU
Using OSX binary.
Server will auto-restart if there is a crash.
Warning: Unable to detour Sys_LoadModule in filesystem_stdio
AppFramework : Unable to load module bin/filesystem_stdio.dylib!
Unable to load interface VFileSystem022 from bin/filesystem_stdio.dylib
Failed to get existing handle for engine.dylib (image not already loaded)
Add "-debug" to the ./srcds_run command line to generate a debug.log to help with solving this problem
Tue 16 Sep 2014 10

9

3 EST: Server restart in 10 seconds
I also attempted downloading the windows version of the GMOD server through SteamCMD, but couldn't find a dedicated.dylib within the server files anywhere.