So, in reading through the “Advanced Client Roaming’ whitepaper (http://www.microsoft.com/downloads/details.aspx?FamilyID=37ac2246-453a-4418-b026-f7140a6fce3c&displaylang=en), I happened upon this section:
You do not need site boundaries if you do not have Legacy Clients (and if you are not using the automated Client Push Installation method). In fact, if you delete your site boundaries, any Legacy Clients will remove SMS
The Roaming Boundaries tab in Site Properties could more properly be called the Advanced Client Boundaries tab. Define roaming boundaries for each site in the hierarchy that supports Advanced Clients, whether they are assigned to that site or may roam there. Roaming boundaries can be IP subnets, Active Directory sites, or IP address ranges. Any given roaming boundary should be used for only one site within the entire SMS hierarchy. Remember that a boundary does not roam; client computers roam.
I have confirmed that this is in fact possible. As my experiences with SMS go back a while, I simply assumed that the most granular you can get with an SMS site boundary was an entire IP subnet (an AD site boundary). I completely overlooked the fact that if all you care about are Advanced clients (which is now more often the case these days then not), you CAN definitely have SMS site boundaries that only include address ranges or even single IP addresses (simply create a boundary that starts and ends on the same address). In a HED environment where you may have many independent departments maintained on the same set of subnets but that want to implement their own SMS sites, this is an important thing to keep in mind as you now can split these machines into their own SMS sites without worrying about site overlap which causes a whole bunch of issues... One caveat of clearing the site boundaries and using just the roaming boundaries for site defitnition is that you cannot utilize Client Push as an installation method. Other then that, you are good to go!
I apologize if I am the only one waking up to this fact - I guess I just got set in using the traditional (legacy) site boundaries and allowing the default which makes the Roaming Boundary a part of the site boundary. It appears that it is in fact legal and supported!!!