True only to the point where the size of the aircraft is comparable to the wavelength of the radar waves. Then size counts more and shape/material properties somewhat less. However a quick search seems to indicate that the Tamara system is passive and really only listens for emissions from the target aircraft. The F-117 produeces very few emmissions, aside from radio calls which can be kept to a minimum. The B-2 does have radar systems, but with GPS it need not use them until just before bombs away if then.
An excellent point that many seem to miss. They have a search RADAR that might detect and track our aircraft. So what, the info would then be sent to a targeting RADAR powerful enough for their beam riding missiles to follow, the Wild Weasels flying high cover would be all over them like ugly on hillary.