Looking at the grade of those ramps, it must have been fun switching in the winter while holding on to several cars. On the other hand, no need for a runaround, just set the car partway up one of those sidings and roll it by.
One correction, the subway crew used switchers - such as S-2's, and in the last few years EMD SW units. I don't recall an RS-1 ever going down there although I'm open to correction. If so, it was an isolated incident and not the normal assigned power.
The power was furnished by NYC/PC, but the crews rotated between NYC, LV, PRR and B&O. When it was an NYC crew, they sometimes brought the train to Goodman St yard with KS-4, the subway crew. When other railroads had the job, the NYC crew picked up the cars from the interchange near where the soccer stadium is supposed to be built, and brought them in.
The grade from Kent Street to the main line at CP34 was quite steep. The crew would assemble the train, often with the cars on the "Abandon", the track which went over to Otis Yard. When they had permission from the dispatcher, they would get a running start down from the Abandon and hope they made it onto the main. Sometimes they stalled and had to try again. More than once, they got hung up, unable to pull out and unable to shove back up the Abandon. In those cases they usually had to cut part of the train and set it on Track 4 west of CP34, then go get the rest.