Is a Grizzly cable just an Ethernet (CAT-5) cable?

No, a Grizzly cable is far different than commercial Ethernet cabling.

A CAT-5 cable is typically un-shielded, provides a balanced signal, and uses different wiring intended for a computer, as opposed to a CNC control.

The Grizzly Cable is shielded, with an ultra-low capacitance, uses unbalanced signals, and is wired for RS232 signals to be sent to and from CNC machines.

CAT-5 cables are unreliable, able to pick up RF noise very easily and have limitations regarding baud rate when running beyond RS232 specifications.