Not sure I understand your question, but... if you're asking if VirtualDub is able to utilize both cpus at the same time then the answer is... maybe 🙂
Not kidding though. I just tested it and I got it using betwen 49% and 57% of my cpus. So in one sense it does seem to use both cpus, but not very well.
Since I'm not an expert, if anyone comes up with a better explanation then go with it. But I'm not sure I understand the relationship between bitrate and smp.😕