On the search to find out how to hide the icon in the Dock of HardwareGrowler, I landed on the blog of an old LUGS colleague Beat: - 0×1b - Hide Dock Icons -

Here are the translated instructions:

  • Open the contents of HardwareGrowler.app
  • Edit Info.plist
  • Insert the following code:
    <key>LSUIElement</key>
<string>1</string>

  • Restart the Application

Now the icon should be disappeared