The DirectVR memory scan is only available in some games (indicated in the top/left corner of the game window if supported).
However, if you are 100% sure that the game handles simultaneous controller and mouse input correctly, you can simply disable the ‘X-Box Gamepad Override’ option on the input page of the menu. If you don’t experience any input weirdness afterwards (e.g. head tracking dropouts, gamepad movement stutter or similarly odd things) all is well and the game in question does indeed correctly handle mouse and gamepad at the same time.
BTW: the built-in gamepad to mouse/kb mapper that makes it possible to use your gamepad together with mouse based head tracking even in games that can’t handle both simultaneously is a fairly feature rich program in itself, the mapping can be fully configured to your liking (also on the input page of the menu).