Seems to me that tesseract does quite a lot of denoising during the layou analysis, like in ccnontextdetect.cpp (thanks to ComputeNoiseDensity method) and in strokewidht.cpp (DetectAndRemoveNosie method).
However, the one thing that I still don't understand is the vigorous_noise_removal method (from textord/makerow.cpp). Seems like it is disabled by default, is that correct? If so, why is that? What does it stand for exactly?