No, HA will not Freeze UI when zwave UInaction performed but what will show in UI will depend on how you display. A switch will toggle immediately but if state of device not matching it will be returned. If showing sensor state of switch(like picture entity that toggle but show switch as sensor) you will not see change(my observations)
When zwave command sent it is still possible to toggle.
I believe zwave is send and respond, so toggle switch (x5) …doesn’t matter UI state showing because in the end zwave will return correct state and UI change to show correct.
For your automation I would have (x2) automations
Automation#1 controls ON/OFF of heater
Automation#2 looks for automation#1 to be triggered the checks pump state ON/OFF and sends notification as needed