I guess the question should be, why are the sites related at all, if you only focus on one type of customer for each "site" with its own "specific domain name?" I assume you are sharing a database and therefore a common server.

Now, if the domain names actually all point to different pages on the same site, you may have some problems with some search engines interpreting these "landing pages" as just that and your site a huge sp@m machine. I don't know.

I just don't know. If the "specific domain" names all resolve to the same server, I think you may have a problem.

__________________
DrTandem's San Diego Web Page Design, drtandem.com