Since Cinema 4D has many parts, that is not simple to answer in general, but as a rule of thumb, if Multithreading makes sense, then it is implemented. It is implemented so well that the app is the core of Cinebench, a widely use performance test.
I wouldn’t dare say that I would know how Houdini is coded in detail and if it uses Multithreading or Multiprocessing for all parts or just a few main parts of the code.
Reading about it in the past, I feel that it is often set as the same in some people’s minds (thread/processors). Anyway, here is how much you can set Cinema 4D into multithreading.
If you have an option to see how much use Cinema 4D has from each core or CPU, then that might help (Activity Monitor). This will then provide a glimpse about the parts Cinema 4D is taking advantage of your Computer, which is the main idea.
Inside of the app are a few parts that are strictly single-threaded, AFAIK. To my knowledge, that is any part of the app that produces information which built up on each other, which sounds to me very logically, or where multithreading would slow down the process, to begin with.
I hope that helps