yes - you can use it outside the domain - however you'll need to configure CRM for an IFD deployment "Internet Facing Deployment" - (This can be used alongside others who are using the standard connection method.)
See
http://support.microsoft.com/kb/948779 for instructions on how to configure CRM for IFD.
Scott Sewell, CustomerEffective | http:\\blog.CustomerEffective.com | Twitter:@ScottSewell