Does it work through the rcon tool on the "Server control" page of your control panel? That tool definitely would send the command to BF3, but I don't know if Procon would.
I just tested it on a server here and it did work.
The "Easy setup" page also runs this command every time it's submitted. If the server chokes on the command, you'll see an error on the response page.
It does appear to have worked through the Server Control page. It was added to the Startup.txt as well.