Sure, but there are many different types of hydraulic fluids and each is a different viscosity specific to the application it was designed for. Plus the add pack is probably completely different.
Here are the specs for JD Hy-Gard. The specs for GM's PS fluid don't seem to be available anywhere.
Viscosity @ 40°C................... 59 cSt
Viscosity @ 100°C................. 9.4 cSt
Viscosity index.................. 140
Density............................. 0.89 g/cm3
Pour point......................... -40°C
Flash point......................... 227°C