I probably don't know the whole Joytech range. The one I know used a Shimano compatible freehub shell.
And AFAIK the 3-tab pattern used for IGHs isn't compatible with the splines for the EGH.
"Splined freewheel" is a strange way of putting it.
Freewheels are generally treated as complete units, clutch and sprockets as one.
And they thread onto the hub.
But take the sprockets OFF the freewheel, and guess what - it's splined.
Freehubs, you treat the clutch mechanism and the sprockets as separate units. And yeah, the sprockets are splined.

Why not post some pics?