If by vowel reduction you also mean phonetic changes, then no, there are no such languages. It's because people always stress certain syllables differently (even such languages as French, which effectively has no PHONEMIC stress on any word in isolation, it does have a phonetic stress on the level of syllables, formulae and phrases, but it's not phonemically distinct in any way). For example, Polish has no PHONEMIC vowel reduction, and all the vowels in each syllable of a given word are pronounced the same in terms of phonemics - and in terms of phonetics, they are ROUGHLY the same. People usually don't spot any difference between the "a"'s in the first and second syllables of the word "tata" (it's pronounced phonemically like this: /'ta.ta/). But because the stress is on the first syllable, only slightly slightly slightly more power is put on the vowel in that syllable, and technically speaking, the second [a] is, first of all, slightly shorter, and second of all, slightly more centralised. But Polish lacks any phonemic distinction between long and short vowels and /a/ is the only phoneme in the slot for //A//, and actually all its allophones are very very veryyyy similar to one another. So in the word /'ta.ta/ above, the first "a" is very close to the cardinal open central unrounded vowel [ä], whereas the second "a" is phonetically between [ä] and [ɐ] (the near-open central vowel). So the difference is so insignificant that nobody can really hear it even on the phonetic level, so effectively, every single allophone of the phoneme /a/ sounds actually the same to the Polish speakers. The word could thus be phonetically described like this: ['täˑ.tɐ˕] (ˑ indicates that [ä] is very slightly lenghthened, and ˕ indicates that [ɐ] is lowered). Actually, all the vowels in the Polish language have allophones which are phonetically very similar to one another, and all are close to their respective phonemic realisations. Maybe that's why Polish has only 6 vowel phonemes while English has 3 or even 4 times more vowel phonemes. Anyway, this was just to give you an example of a language which lacks a phonemic vowel reduction but still has a phonetic one (every single language has it, even the ones with allophones so close to one another as in Polish). Long story short, it is impossible NOT to have a phonetic vowel reduction because every language has prosody, which yields suprasegmentals and relative articulation (UNMARKED articulation of the same phoneme in a neutral sound environment).