You can't use the asrock itx mobo with the NH-D14 or any other for that matter. It doesn't use the traditional backplate and they installed chips on the backside of the mounting area. Therefore, all aftermarket coolers needing a backplate will not work without some creative workarounds, spacers, etc.
I have the A88X Gigabyte itx mobo and it along with the MSI version are only ones that can take on after market coolers. If you click on my blog in my sig you can scroll down to see a picture of a Noctua U12S installed.
As far as your question is concerned, it will blow towards the rear properly mounted. Noctua has tremendous documentation and a downloadable pdf for you to see yourself.