Does NS and/or CSX still use the old Conrail train symbols like TV-4 and INCO?
No, to a point.
CSX has their wacky letter with number symbols like Q273 or K650. They're supposed to inplement a six letter system in the next year or two similiar to BNSF, but still retain their current system.
NS uses two numbers and a letter, 20A or 11J, but I also occaisionally hear trains using old Conrail symbols such as TV214.