Yes, /ʌ/ can become /ə/. Similarly, aspirated stops can become less aspirated. Both are related, since the results are due to whether stressed syllables are accented or not.
The gradation goes like thus:
Nuclear pitch accent > pre-nuclear pitch accent > unaccented (no pitch change) > reduced > dropped (syncope)
For instance, look at the phrase "absolutely right". If each word in that phrase becomes its own chunk, we are left with "absolutely | right". In that case, lexical stress is retained and pitch accented. When one utters with one chunk, as heard on talk shows, one hears like "absly RIGHT": in this phrase, one hears primary stressed /æ/ vowel, the secondary stressed vowel /u/ is lost, and there is a pitch change on /aɪ/.
Similarly, aspirated stops can become unaspirated, depending on how speech is chunked (rhythmed).
That's why it is fallacious to claim that English is a stress timed language. Peter Roach showed that stress timed English doesn't sound native (check his youtube on Intonation). English is an accent timed language or tunit-timed language. Many voice over actors, impersonators, impressionists recognized this long time before the EFL instruction. But they don't use the same concepts. Instead, they use devices like "da da DA da". Frank Caliendo, who impersonates Dubbya Bush, John Madden, Charles Barkely, etc, claims he is working on Obama's impersonation, but couldn't get it right, since Obama has a distinct way of chunking speech.
