Hi HopeCreek, and welcome to the site.
You are correct that some polled animals exhibit scurs. The gene responsible for scurs is on a different location of the DNA than the gene for polled/horned. These two traits are not connected. A certain percentage of horned animals also have the gene for scurs. If you let the horns grow, you cannot see the scur because the horn growth covers it up. If you dehorn a horned animal with scurs, the scurs are removed with the horns. Therefore, you never see the scur trait in horned animals, even when it is present.
I've seen scurs in polled Jerseys and polled Herefords. I have had one Jersey bull and one Jersey heifer with scurs. Scurs are not attached to the scull and do not grow outward like horns. You can wiggle them and they do not get to be more than an inch in length. I have posted a couple pictures of my heifer with scurs down below. She is two years old and will calve soon.

- 019 (Medium).jpg (86.93 KiB) Viewed 23753 times

- 021 (Medium).jpg (156.46 KiB) Viewed 23753 times
An animal with scurs is polled and a percentage of the resulting offspring will also be polled, with the polled percentage dependent on the homozygous/heterozygous status of the animals. It is also the same with the scur trait. The percentage will depend If the animals are homozygous scurred or heterzygous scurred. You could have an animal that is homozygous for both. You could have an animal that is homo for one and hetero for the other. Another animal could be free of one and homo or hetero for the other. Because the scur trait is hidden in horned animals, it is difficult to predict the percentages.
There are some people out there that will not use a bull that has scurs and this will help eliminate the scur trait. Personally, I feel that if I had the choice of using a lower valued scur-free bull and a higher value scurred bull, then I would use the higher value bull. If they were of equal value, I would choose the scur-free bull.
Thanks for bringing this topic up. It is a confusing subject and I hope that I helped clear it up a little.