They don't have customer key access and can't assume customer identity but ultimately yes, via a multi-eye approval process there is access to the prod infra - but this is extremely tightly secured, and not something a phishing attack on a single sales engineer could ever achieve.

Many enterprise customers additionally use standard third party crypto libraries to tokenise and/or encrypt sensitive fields before storage in any warehouse/database such as Snowflake or Redshift.

This is a similar principle to using client-side encryption for S3. The infra provider (AWS in that case) can never read the data.