No, it's will not be available.
Look, a game client it's like a fashionable dress weared on human which know french language, if you will wear italian shoes you will not know italian language.
The game client it's just visual part, you can or can't have this visual part. The whole logic at server-side. And server-side must works in pair with client-side.
2015-11-04aRagexe contains inside LOGIC how to manipulate graphical content and present it to end player. The game client works know how to display sprites, what will happen when the char will move, know how to display effects and so on, it's everything hidden from our look and we CAN'T manipulate or change it, because it's inside exe very deeply. But game client knows nothing about monsters, their logic and so on, everything for clients just a files, and some logic. Only with server-side communication via network the game client and server begin work. Server-side calculate mechanic, moving chars, and sending to game client where need to move a sprite, and update positions and so on to end user. It's very long story, just find info about any mmorpg or client-server games info, and you will get the whole idea, here is nothing different too.
// means -> comment. Comment means -> Do not load everything after this symbols in the line.
If you will remove these symbols, the line will be loaded. But in your case, this is just a comment for devs which made devs some time ago for their self to not forget about adding a new mob. If you will uncomment (remove these // symbols) nothing will be changed, and you will see an error at map-server, because this line is not valid for mob_db.txt data format (read comment of the file in the top of the file)