5.6V RS232 Signal OK Without Level Shifter?

Im linking up two Arduino Megas over a ethernet bridge, this happens to have a serial RS232 bridge on it as well. Ive saturated the ethernet part, so my Arduino to Arduino communication will be over the serial link.

Documentation for the link, and testing with multimeter the RS232 signal is at 5.6V. I noted online it says be careful as a lot of RS232 is 12v and will damage the Arduino. Also that the Arduino in those situations needs a level shifter to bring it down to 5v.

Question is, is 5.6v ok, or do I still need a level shifter?

and -5.6 V
use MAX232 conversion chip

Perfect, thank you, will do.

On the mega which also has a few more hardware serial ports on the board. I know using software serial to use other pins you define it etc. But I read for using multiple hardware serials, you can do away with all the software serial side of things.

Question is, why wont it all get confused? In my example, the air end is writing out VISCA camera commands on the main hardware serial, if I now hook up my communications to the other hardware serial ports, and don't have a way of distinguishing between them in code, will it just work?

EDIT: just realised when using multiple hardware serials it is Serial, Serial1, Serial2 etc etc!