Creating "derivative" products within the limits of free use (analysis, satire, re-mix) should be totally OK. Anything that's original work has even more protection.
DMCA provides a safe-harbor clause to content hosters - which is what FAKKU is for content uploaded by the users - and the only requirement is remove any content the host owner *knows* to be violating copyright law, as well as to comply with DMCA take-down notices that inform him of such violations.
It is *not* the hoster's responsibility to monitor user generated/uploaded content, but the copy-right owners to do the monitoring and notify hosters when a violation occurs.
In your case, FAKKU can claim to have acted in good faith, as derivative works are protected under fair use.
PS: IANAL, so take all of this with a pinch of salt.