I live in the United States and am trying to setup and maintain an entirely legal set-up. As a result, I recently purchased Fluendo's complete codec pack.

Afterwards, I stumbled on this forum post. viewtopic.php?f=116&t=69292&p=99293&hilit=fluendo+legal#p99293

I'm not sure what to make of this. Am I safe to use Amarok with these purchased codecs?

Amarok doesn't do any decoding or encoding, so there is no legal concern. Of course you are always save with legally purchased software, be this codecs or other.