Here is a workaround to launch an external script to hide the DOS box. The idea is very simple: you use a Visual Basic script that runs the batch file in the background, thus effectively hiding all output!
The VBScript code is a single line and as follows:
CreateObject("Wscript.Shell").Run WScript.Arguments(0), 0, FalseSave this file as HideDOS.vbs on your content share, for example in the Tools folder or something. Then call your external script called G:\Doit.bat using the following syntax:
<SCRIPT TIMING="PRE" EVENT="LAUNCH" WAIT="TRUE" PROTECT="TRUE">
<HREF>wscript \\server\content\Tools\HideDOS.vbs G:\Doit.bat</HREF>
There you go, gone is the DOS box!