Hi Margie,
You can absolutely match things using the de-duplication rules but you'll have to be a bit creative about it. The way I've seen it done best involves creating a master list of domains that you consider to be the "account" domain (so for example you'd want to weed out gmail, yahoo, hotmail, etc. so that they don't inadvertently link your corporate domains with people's personal emails, etc.) and build out a scheduled process for updating that list maybe quarterly (depending on how fast your database grows). Then you'd need to set up a process in Program Builder using the de-duplication rules to "match" domains from the contact record in Eloqua to the Account table. Where it could be very powerful is in "mapping" your SFDC leads to their prospective accounts by writing the linkage back once you've matched them correctly inside of Eloqua.
Best,
Lauren