one site, multiple domains?

We're planning on having 2 or three sites on our MOSS server farm.

One is our intranet portal. One is our team site collaboration portal and
the 3rd would be our mysites portal.

We'd like to have 3 subdomains to point at each of these sites:

intranet.ourdomain.com
teams.ourdomain.com
mysites.ourdomain.com

That sounds pretty straight forward.

The catch is that we're going to have a standalone server INSIDE our
firewall that is going to be used for site admins to add people to their
sites. The reason is that this inside server will be able to use the AD
address book, and it will be set up so that people can add folks to our DMZ
AD domain. I'm not a networking guy, but I'm told we're doing this mainly
for security reasons and for reasons to do with just how our network is set
up.

So, my question...for this 4th 'admin' server, can I have one domain, such
as SPadmin.ourdomain.com point at the content of all 3 above mentioned
portals? Or will this 4th server also have to have all 3 sites extended to
it and set up with 3 unique domains?

-Darrel