Well, yes. So now I am confused
as to what you originally meant.
Sure, the workstations should point to your DNS server(s) only. No, one should never mix DNS addresses in any environment.
Doesn't that mean all internet DNS queries will go to the server and it will send all unkown host names upline and then cache the answers?
Absolutely. Records will be cached until the TTL runs out. If this is what you mean by " serving up addresses for every one of the thousands of banner ads", then yes, your server is doing that. I don't think it inappropriate for a local resolver to do so. And, if the workstations are running the DNS client service, those records are cached at the workstation, and your server will not be queried. The browser cache also tends to eliminate such repeat queries as well.
As to whether one finds the type and amount of advertising on the net to be appropriate, or just annoying, or a bandwidth hog, that is mostly a personal preference. Which is why, for reasons of efficiency, I suggest blocking such junk locally, at the browser. That way, nary a lookup is raised for such.
