According to Rich Skrenta, one of the DMOZ founders, that's exactly what happened. Server crashed, no backups and "during unsuccessful attempts to restore some of the lost data, ops blew away the rest of the existing data on the system." He thinks that they're currently trying to recover stuff from the last RDF dump.
He doesn't hold out much hope for DMOZ's survival under AOL and sounds pretty glum for its continued existence at all.
[Heads up, Webwork, link drop to somebody elses personal blog on the way, though I do think it can be considered somewhat authoritative ;-)]
Rick Skrenta: RIP DMOZ 1998-2006 [skrenta.com]