"The white hedgehog hikes often" should be a better translation than "...is often hiking."
why won't it accept 'the white hedgehog often hikes'? also, when will I ever need to say this in Korean?
등산하고 있어요 is present progressive, so the correct translation is "hiking" rather than "hikes".
No one expects you to repeat these sentences to anyone, but it's useful to see how the sentences are structured and to learn the grammar points so that when you come to make your own actual sentences in Korean you will know how to structure them.
My larger issue is how could a language not differentiate between mountain climbing and hiking? Wouldn't the better term for hiking be 도보 여행 or do Koreans really just usually call it rock climbing (which requires rocks, much better physical fitness, proper clothes and typically equipment)?