Hey uOpt--thanks for this reply.
My take away from your comment is that having a consumer-level graphics card with two outputs could be mildly dangerous because it, like the motherboard, could be susceptible to RAM errors and could blue-screen the server.
Say you wanted to be safe--would you install two separate video cards of the nVidia Quadro or AMD FirePro variety? If not in a 3-4U case, would they go on two risers on a 2U? If I ran a new CPU with the very newest (fastest!) built-in Intel GPU, could I install only one extra graphics card and use both at the same time?