I didn't see this, no, but I don't often visit the DMOZ website. I tried some quick searches for you:

The Internet Archive for some reason stopped archiving at the end of February:

http://web.archive.org/.../http://www.dmoz.org

But a quick search over at Google did confirm your suspicion - you weren't imagining things!

http://www.timbooker.co.uk/stuff/mdp.png
http://searchenginewatch.com/...ort/02/04-fools.html

Talking about Google and April's Fools .. this was a classic from Google:

http://www.google.com/mentalplex/

- wil