Not always. If a piece is real driftwood that has been submerged for a long period of time, the tannins might be gone. I have several pieces from local creeks and rivers (blackwater river/ coldwater creek) that have never released tannins.
Having tannins in the water is mostly just an aesthetic issue anyhow, a lot of the fish that we keep are originally from waters that have some tannins in them.
As far as disinfecting the new wood, boiling usually does the trick, but I usually get my pieces from a collector that lets them sit out in the sun for a year and then into dry outdoor storage, so there's not much chance of anything living making it to the tank. I would think that boiling for a few hours would serve the same purpose in that regard.