Vietnam is on the cusp of joining the emerging-markets club and stocks have notched their biggest rally in years, but foreigners have been sellers and say investing is handicapped by tariff risks, ownership limits and one firm&#39;s dominance of the index.

Vietnam is on the cusp of joining the emerging-markets club and stocks have notched their biggest rally in years, but foreigners have been sellers and say investing is handicapped by tariff risks, ownership limits and one firm's dominance of the index.