Is down voting open to scrutiny at any level?
While the intent of the question may have been to ask about mandatory commenting on casting a downvote, it actually asks a different question to which an answer might be useful.
Yes. Downvoting is open to scrutiny but only to Community Managers† and Stack Exchange staff†. There is no reputation level which allows access to voter identity.
Moderators have some limited tools to examine vote patterns, but can’t see who cast which individual votes. Suspicious vote patterns are submitted to CMs for detailed investigation.
Voting is never truly anonymous, or rep lost with downvotes on answers which are subsequently deleted could never be refunded. There’s also a nightly job which examines voting and can invalidate certain votes (such as obvious revenge downvoting) automatically. The effect of revenge downvoting, and that it was done, can be seen by anyone; but only the auto job and CMs know who did it.
† Community Managers’ and staffers’ contributions on the site are identified with a diamond as if they were moderators (which they are) but they are not listed with the site-elected moderators. Further reading