Yes, but most of those 34 fell during the Linebacker II campaign at the end of the war. prior to that I want to say less than 5 were downed by Viet air defenses. And had the B-52 been employed in 1964/1965 ike the JCS wanted to do before the air defenses were so tough it likely would have been far less. The heaviest losses in Linebacker II were due to two primary reasons:1) the use of G & H model B-52s that did not have as comprehensive of defensive ECM suites as the already in Theater D models, and 2) the early use of repetitive tactics, flight routes, etc. that allowed the Viets to know where follow on waves would be coming and concentrate their defences accordingly. By the end of Linebacker II revised tactics had dropped losses to 0 and the Viets had fired up all of their SAMs. Then they went back to the negotiating table.
Vietnamese air defences were allowed to evolve into what they became due to ludicrous rules of engagement drawn up by the White House. They could have been smashed at the railhead and dockside if allowed in 1964/1965. Those lessons were well learned and applied in 1991.