If you disable the "Enable joystick global buttons" option, enable listening manually so it remains enabled, run the game, hold down that same joystick button, and speak a command, does the command have any effect ingame?
If you physically press the key the command would be pressing while you hold down the joystick button, does that have the expected effect ingame?
If you open the "CONTROLS" tab of the settings in DCS, choose the aircraft your commands are intended for in the top-left dropdown, and execute a command, does a blue highlight jump to the relevant binding in the list?
If you click the "Modifiers" button on that same tab, near the bottom left, just above the "CANCEL" button, are there any joystick buttons listed?
How long are your keypress actions holding the keys down? Have you tried running VoiceAttack as administrator?