Wikipedia claims that Von Neumann and Klaus Fuchs also had a preliminary design for a hydrogen bomb that also used the implosion bomb as a first stage, though in a different way than the Teller-Ulam design. Fuchs leaked the Neumann-Fuchs design to the Soviets along with everything else, but just like the US, the Soviets set it aside and independently came up with the Teller-Ulam design instead. So it would seem that, despite Teller and Ulam winning out, Von Neumann was still deeply involved in hydrogen bomb development beyond simply developing the prerequisite plutonium implosion bomb.