Whatever $DOSProg is, perl.exe (a console application) has little or no control over it. wperl.exe (a windows application) has the same amount of control. What makes console applications special is that they won't open a new console window if invoked through the command interpreter (cmd.exe or command.com). So the only way to hide this other window is depends on

cmd.exe /?
command.com /?
[download]

and your ability to modify $DOSProg (exetype, exe_update), or your knowledge of the Win32 API, neither of which have much to do with perl.