Ok, I've got the thing downloaded. I noticed the launcher for it acts as the OB exe itself... can I not use it with the Oblivion Mod Manager? Because some of the mods I'm, well, managing, are supposed to use OBSE...so... what to do?
You don't need to use the Launch Oblivion button in OBMM for any reason. It won't affect anything to use the OBSE_loader.exe directly.
That said, if OBSE is installed, then OBMM will automatically use the OBSE_loader.exe when you push the "Launch Oblivion" button. So either way you should be good.