What you describe is typically called a "single label domain" in Microsoft AD speak. You'll find that you have app compat issues as many apps make assumptions when presented with "domain" that does not have a period in it...namely, that it isn't a valid DNS domain.
So I wouldn't recommend doing this directly even though it's possible.
That said, there are a couple of other options fo ryou, depending upon your exact goal:
- You can make hostname resolution work (ie "ping host") by just configuring DNS correctly. It would append the suffix of domain.com automagically. Maybe this is good enough?
- You can use Netbios name resolution (typically people refer to this via an old service that implements it, called WINS) to get hostname resolution (ie make "ping host" work). By setting up WINS (typically done on the same boxes that host DNS, though not required) & having your clients register WINS records, this would start working for you. The advantage of this over DNS is that this can work across many DNS namespaces with flexibilities not often afforded to DNS (yes, yes, there are other options in modern DNS, like resolution across namespaces, global zones, etc....but it's out there).
- You can register records in a different namespace named just "domain" and host this on your DNS servers, then register records in to it for your boxes. I'll admit I haven't configured this myself but in theory this should work. I'd be curious if ti doesn't (I can imagine a few edge cases that might be problematic, like Kerb mutual auth, if you rely on such things for your scenarios).