Yes, pointer devices such as a mouse or a touch screen can be used to drive on iRacing. Your driving experience may not be as enhanced as it would be with a Wheel and Pedal set however After launching the simulator, click the calibrate button at the top of the screen and follow the on screen instructions. Click on the drop down arrow and choose "Use touch/mouse for steering" and click done. Follow the onscreen instructions.
You can modify the sensitivity on the F9 black box while driving.
There are also other more extensive settings in your app.ini file (located in your Documents/iRacing folder) that lets you customize how mouse driving works.