We are very excited because as of right now the next release of J!WHMCS Integrator (2.4.9) DOES support Joomla! 3.0... I have gone in and tested the entire package, rewritten a number of key functions to ensure compatibility and have tested on Joomla! 1.5, 2.5 and 3.0alpha 2... beta testing is next up.
The product will be ready when Joomla! announces it's release - so in short "Yes!"