You're correct that this would fail a fair-use test. Once it went up on a blog it's akin to a public performance, and use of the master recording should be licensed.

It is improbable that someone is going to issue a DMCA letter because of this, but it does (to your point) outline a couple of problems in S.V., one of which is the misconception that "It's not stealing if you attribute the artist" is widespread. And incorrect, at least for anything (c)All Rights Reserved.

If in doubt, it's a good idea for startups to consult their attorney (and not the PM, or lead engineer, or friend-in-a-band) when in doubt when using music, art, or what-have-you in public fora.