IMO the BT are no worse and maybe a little bettter than a soft point in not deflecting on brush.
YES!
A bullet that is slipstream designed to buck wind will probably be a bit less effected by brush as well.
Will they expand prematurely? Or do they perform like a normal soft point when they contact brush?
It will probably vary. I've heard of soft point bullets fragenting and/or mushrooming when hitting brush giving poor performance when hitting an animal. Best bet is to not shoot through brush with any bullet.