Yes, but it is not the default mode of SIGNL4. The default mode is single-ack, i.e. only one person needs to acknowledge an alert.
You can switch any time between 'all on duty need to ack' and ‘first come, first confirm’ mode; in the later case only one person on duty needs to confirm an alert. This is often used in maintenance scenarios or IT operations. The multi-ack mode means that the number of people who are currently on duty needs to confirm. If you have 3 people on duty at the time of the alert, you need 3 acknowledgements. But not necessarily from the same persons who are on duty. This provides for greater flexibility.
You can change the alerting mode in the management portal of SIGNL4 under 'My Team' (https://account.signl4.com/manage/)