Aoife has the core of it.
Cutting the solenoid only puts the directional valve into its rest position. Depending on the valve type that can trap air in the cylinder (closed-centre 5/3 valves do exactly that), so the cylinder can still move when someone opens a fitting, or hold a load that drops later. A stuck valve spool is the other failure: power off, valve doesn’t move. Pneumatic energy is stored energy, and for safe access you want it gone, not held. The dump valve exhausts the supply to atmosphere so the cell ends up at zero pressure. The safety relay usually also monitors the dump valve’s feedback (a pressure switch or a position contact), so a dump valve that fails to vent stops the cell from restarting. The two parts cover different failures. How much of this you need follows from the risk assessment and the required performance level under ISO 13849, which is your engineer’s job to document.
On Hermetry Safe: there’s no doc page for it, so I won’t guess what it does. Whatever it does, I would never put a cloud platform into the safety function itself. Even the personnel tracking page calls that solution an information tool, not a certified safety system. Emergency stop, safety relay and dump valve stay hardwired.
What works today and is useful: monitoring. Wire the safety relay’s auxiliary contact and the dump valve’s pressure switch into the cell PLC or a gateway and send them as telemetry, say estop.active and dump.vented. Then an alarm rule can tell maintenance when the e-stop has been active for a long time, or when the e-stop is active and dump.vented is still 0. That gives you records and notifications without touching the safety chain.