I haven't had time to dig through the entire LISP for Mac Developer Documentation, but obviously there are no ActiveX functions provided (i.e., GetOrCreateObject, GetInterfaceObject, etc.), in order to access Shell.
Further, there is no Shell Command for Mac... Perhaps I've overlooked something, someone more knowledgeable than I at AutoCAD for Mac will know of.
Otherwise, it looks like you're relegated to using Terminal manually, whilst waiting for Autodesk to offer a Cocoa, XCode, etc. adaptation to their APIs.