Does anyone know if patch 1.6 will be released before dawnguard, or in addition to dawnguard?

I think it'll be the Dawnguard patch.
As for mounted combat, it's ridiculous with a one handed weapon, almost impossible to hit things.

you know if you can use two handed weps? i havent seen footage of anything but one hand n bows/x-bows

The Dawnguard trailer featured mounted combat at one scene, which leads me to believe that it should be released to consoles prior to or with the DLC.

Yes you can.