Could processing in Vissim be distributed using someing like this: http://www.boxxtech.com/products/renderboxx
Most probably, such a hardware won't help much for distributing single simulation runs because the necessary communication overhead is just too much. We haven't yet seen a dual-processor machine which beats the fastest single-processor machines in Vissim simulation speed. For multiple parallel simulation runs such a machine (with multiple modules!) can be used better, but multiple fast single-processor computers in a network still should be faster.