I can state from personal experience that a DU bushing will not need resizing for installation purposes after it's been pressed into the rocker. I can also state that if no other changes are made, it won't last all that long. I got about 12,000 miles out of mine (lots of track time in there) and had wear >0.01" on one of the bushings.
I know that other folks have gotten DU bishings to work quite well, even on race engines, but these folks cut additional oil grooves, they enlarge the bore slightly by honing (DU expands a lot when hot, so it needs more clearance so it doesn't cut off its own oil supply), and they polish the rocker shafts to a very smooth finish so the teflon coating is not abraded. If you are disinclined to do this, then DU is probably not the right stuff for you.
As far as refacing the rockers, I am not sure the processes used are of sufficient accuracy to make much difference. After the DU bushings wore out, I had a set of mine rebushed with bronze and refaced, and the contact area on the camshaft appears to be anything but even. This is after about 1800 miles of driving, maybe 200 of it track time. Contact is clearly not even across the pad.
Bronze bushing wear after 1800 miles is visible, but not really measurable, so it's <= 0.001".
