Yes, the Swedish O can be either /ʊ/ ("hook") or /u:/ ("boot"), or /ɔ/ ("not") or /o:/ ("yawn") This is due to a vowel change hundreds of years ago. It's not a matter of long vs short, since it can appear in any of the forms. Generally, it takes a /ʊ/ sound (short "oo") at the beginning and end of words, and an /ɔ/ or /o:/ sound otherwise. Also, stressed open syllables on -o are usually /u:/. But that only a very broad generalization, and you'll have to learn which ones are which way.