HI man, i think this type of machines simply donīt need the spindle to be controlled by mach 3, becauses is single tool, and usually you go with the same rpm with the same tool. I had this question also, and the manufacturer told me that i have to turn on/off the spindle manually on the VFC. Yes, it sucks, i know, but the M3 M4 M5 g code wonīt work because simply there is no connection on the pins/ports. At least this is the case with my nes HY6040.I think you can do some wiring to correct this, but im not expert in electronics.
Hope it helps!