Yes. Allen Bradley to my knowledge always starts their Channels at Zero, which is always a Serial Port. This applies to their standard PLCs like the MicroLogix, SLC500, and PLC5. Things are a little different with the PACs, like the Logix Family. Although, they too have Serial Ports on a number of them.
What Channel 1 is will depend on the Model of PLC. It could be another Serial, DH485, DH+, RIO, or Ethernet Port.