I'm pretty sure that if the Ukrainian is hyphenated, my answer can be hyphenated as well. That being said, 8-18-15: reported and not corrected.
well... the hyphen sort of replaces the verb to be in Ukrainian as I understand it, so if you're translating properly in english, you should use "my hobby is web design", not "my hobby - web design" because the latter doesn't make sense in english.
Got it. The hyphen is kind of a lazy replacement for various things in English as well as a means of linking things. So I'm not sure.
In Ukrainian we omit the word "to be" in present tense. The hyphen is not necessary on Duolingo, if you skip it, your answer will still be accepted ("Моє хобі вебдизайн"). However, skipping "to be" in English is not grammatical.