daz3nt,
You can run the engine without the spinner without any issues. You do get a couple of small benefits from having one. First is that the spinner actually covers up the root portion of the propeller. This portion of the propeller actually causes drag and can reduce the overall output of the prop. By putting the spinner on you cover up the portion of the prop that causes these problems. Second, with the spinner you get a small amount of flywheel effect which can help the engine run smoother at lower RPM's. Are these factors huge? Not at all. In fact you may not even notice the benefits, so it's not necessary to do it.

But from your pictures you need to decide one way or the other. You will either need to put the backplate on the spinner, or remove the spinner completely. Trying to run the engine like you have in the pictures could be dangerous.

Ken