I can certainly understand why what you see on your Knockout rose might look like it has rose rosette disease. My guess is that it does not.
As Porkpal said: For many roses it is normal for new growth to have a purplish hue. In my garden Europeana and Double Delight both have it. It is also normal for new growth to be a little distorted, especially if the rose is growing quickly. The roses with RR appear to be covered with distorted leaves. On your rose there is a lot of normal-looking fresh new foliage. Also, it looks to me like the Knockout foliage in the photos of RR disease is more red than purple. Not sure that's an important distinction.
If you get to a point in the summer where your roses are taking a break but the distortion and discoloration persist, I think I would have it checked out by someone who actually knows something about RR.
