When rigid tapping in a fully synchronized system ER Tap collets provide zero movement with no axial play. While Quick Change RT & RA are called “rigid” they still have some movement in the Quick Change connection which can cause some issues.
RT holders do have a hole thru the center for coolant, it is not sealed but works well with the appropriate adapter. Most RA adapters allow coolant to the back of the tap , the exception is some of the pipe adapters have a stop plug that needs to be modified. This is not a sealed system but fluid dynamics apply, if the outlet coolant hole is larger than the inlet coolant hole there is no issue. Leakage occurs when the outlet coolant hole is smaller than the inlet causing back pressure. This back pressure will leak out of the mechanism.