I've done a few hundred barrels, so here is my two cents...
Yes, the bore needs to be concentric. Using a live center is the way to go...the only way to go really.
You don't really want to use the center itself, it is hardened steel and it will mess up the crown. First you need to make a centering spud from brass. Cut it so that it has both a 60 degree included taper on both the inside and the outside. You can do this easily by using a center-drill for the inner diameter and using the compound to cut the outer diameter.
Cut it with a post that is the same size as the bore diameter.
Slip this contraption over the center itself, while using the barrel to hold it in place. What you'll have is the spud inside of the barrel, (it only needs to be 1/4" long) and the brass centering up the barrel on the live center itself.
This does three things. One, it protects the rifling inside the barrel and two, it allows you to re-crown the barrel without cutting into the live center and it also centers the barrel up on the bore.
More often than not, the O.D. of the barrel will be a few thousandths off center. No big deal, just cut to the major diameter of the thread that you need. Be sure to use a parting tool to cut a relief in the threads so that the suppressor can shoulder up and tighten on the barrel itself, not the end of the threads. The shoulder must be absolutely perpendicular to the bore, because this is where the silencers both tightens up and aligns itself.
If you have concentric threads, and a square and perpendicular shoulder in which to align the suppressor on, you will have no issues with misalignment.
AR CHL inst.