I fully agree with Incrediblehelps' theory.
I understand that you do not wished to have the IP/DNS indexed by the SE's (how did you find this out anyway - random search?
As I see it you have two options:
1 - request (or adminster) a change of server - then resubmit the URL to the SE's. If the IP gets reindexed again - the integrity of the server of software may be in question.
2 - If the site has confidential content (refer to the companies security classification policy) it should either be hosted on a secure intranet (not extranet) or as some of the larger corporates do simply mask the address (you need to discuss this with the infrastructure/server manufacturers)
Just to put the cat amongst the pigeons there is a rumour that having a unique IP address can help with search engine ranking. A number of hosts don't give out unique IP addresses to save money, and assign the same IP to multiple domain names.
A good check point is to go to
http://www.name-space.com/search and enter your URL in the nslookup field to get the IP. Then re-enter that IP in the browser. If another website or an error message appears youprobably share your IP address.
Steve.