That the Southern assigned engines to a particular subsidiary did not mean that they were limited to that subsidiary–or even ran on that subsidiary.
I did not see the Tennesean often when I was in Bristol from 1954 on (its timing interfered with college)–but every time I saw it, it had PA’s until the Southern engines began running through from Washington to Memphis, Birmingham, and New Orleans–and I saw only EMD products on the Pelican and Birmingham Special.
The EL PAs would often arrive in Chicago in the AM after handling an overnight passenger, then would run a transfer job over to Clearing before returning to handle the passenger train going east. They could fairly reliably be seen at Hayford heading into Clearing around 10A in the early 60s.