Not true. Espee did specify " run - through " dynamic brake circuits on their SW - 1500's, which would allow them to pass signals through to the rest of the engines. The bigger issues with most switchers is the lack of alignment control couplers, and lack of a toilet. This limits them to being buried in consist on road freights.
Most railroads did not recognize the benefits of dynamic brakes until the 2nd generation of diesels appeared; also some RR's in the Midwest, like Rock Island, refused to equip any of their engines with them. Rock Island even went so far as to remove dynamic brakes from the E's & F's they bought second - hand from EwePee.