Three phase systems - when is potential of a star node equal to zero?
Assuming that the three feed voltages are balanced and are sine waves i.e. line voltages are identical with exactly 120 degrees between them, any star connected load of equal values will produce 0 volts at the star point. This means that three identical resistors will yield 0 volts AND three identical inductors (or capacitors) will also yield 0 volts.

With zero volts between a star network of resistors and a star network of (say) inductors, connecting those nodes will not cause a current to flow hence, they can be connected.