Can I use Cat5 wire for a communicating thermostat?

I currently have an Ecobee connected to my Gree Flexx Ultra R32 using 24V. However, the installer also gave me a WK-010WC1 thermostat which supposedly can operate in 24V or communicating mode.

If I replace the Ecobee with the communicating thermostat:

1. Can I reuse two of the existing thermostat wires for the H1/H2 wires?
2. Or can I run Cat5 cable (which I have lots of)? The spec in the manual is:

Light/ordinary PVC sheathed twisted-copper cord L 30 Cord size (mm2) (2×0.75~ 2×1.25) The total length of communication cables can't exceed 30m.