From http://www.waveprotocol.org/draft-protocol-spec it's clear that Wave is 100...

ruslan on June 7, 2009 | parent | context | favorite | on: 5 very detailed posts analyzing Google Wave

From http://www.waveprotocol.org/draft-protocol-spec it's clear that Wave is 100% based on XMPP, which means contact authentication prior to communication takes place, hence there's no room for spam in Wave/XMPP (at least in esteblished meaning of 'spam').