We've never had a problem with our tandem touring wheels from Thorn, or the wheel built by JD cycles on the Santana. After several years of faithful service, the wheel we had built by Spa has broken 3 spokes this year (two of which occurred in the first 100 miles of a 1200km ride). Not sure why...
I'd certainly recommend both Thorn and JD cycles. We are not the heaviest team in the world, but our wheels do quite a lot of miles and are not treated gently.