You're right about different sources. You're wrong about agendas, with possibly one exception.
I would imagine, if OB uses Bellmont or UT admin as sources then 1) it's not a good source, and 2) there is likely some message control going on. The reason it's not a good source is what you're seeing already. In the last few days, we've seen folks there at that site ALL OVER THE PLACE with what they're saying. This sounds like Belmont to me, as anyone who gets a call from Patterson will appear to be in Patterson's crosshairs when that's not necessarily the case at all.
Elsewhere, let's take JS for example. His source has been with him for quite some time. The info he gives in no way provides benefit to his source. In the latest case, it actually made him look bad (Black Friday) at one time. I see no agenda in what and how he operates. He's just got a great window into the back rooms of these dealings.
McPhaul does have a source that he suspects might have some Mack influence affecting the news he gets from them. Otherwise, I think it's very safe to say he's getting pure info unaffected by opinion through his other sources.
One thing I do know about these BMDs from observing their words/actions - they're not used to being wrong about anything. For that reason, you usually just get the truth as they know it.