Does Amazon Redshift support MVCC?
I found an answer in Redshift documentation soon after asking the question. The chapter is called Managing Concurrent Write Operations:

Amazon Redshift allows tables to be read while they are being incrementally loaded or modified.
In some traditional data warehousing and business intelligence applications, the database is available to users only when the nightly load is complete. In such cases, no updates are allowed during regular work hours, when analytic queries are run and reports are generated; however, an increasing number of applications remain live for long periods of the day or even all day, making the notion of a load window obsolete.
Amazon Redshift supports these types of applications by allowing tables to be read while they are being incrementally loaded or modified. Queries simply see the latest committed version, or snapshot, of the data, rather than waiting for the next version to be committed.

That corresponds to MVCC definition from Wikipedia:

MVCC [...] approach: each user connected to the database sees a snapshot of the database at a particular instant in time. Any changes made by a writer will not be seen by other users of the database until the changes have been completed (or, in database terms: until the transaction has been committed.)
When an MVCC database needs to update an item of data, it will not overwrite the old data with new data, but instead marks the old data as obsolete and adds the newer version elsewhere. Thus there are multiple versions stored, but only one is the latest. This allows readers to access the data that was there when they began reading, even if it was modified or deleted part way through by someone else.

Connected with Redshift vacuuming description that I posted in the question, it makes me believe Amazon Redshift does support MVCC. Although I still was not able to find any mention of MVCC in official docs for Redshift.