Does RedHat Linux 6.6 require realport driver for a serial printer?

Realport
1

Digi TS8 & TS4 units Serial printers set comms xon/xoff handshaking.

2

You could use LPD instead of installing a driver:

http://knowledge.digi.com/articles/Knowledge_Base_Article/HOW-TO-LPD-remote-printing-configuration-with-UNIX-Linux