Samsung says SmartThings isn’t suitable for commercial use as it isn’t reliable enough. They specifically mention food spoilage.
Data accuracy and consistency from SmartThings sensors, including those provided by SmartThings directly, resold by SmartThings, or supported by SmartThings, is not guaranteed. Therefore, you should not rely on that data for any use that impacts health, safety, security, property or financial interests. For example, because temperature readings may vary significantly from reading to reading on an individual device, between devices, or over time, those readings should not be used to control heating and cooling in environments where food spoilage, health risks, or damage to physical goods could occur.
Also, the most common reason for freezers to fail is a power outage, and at that point it’s very hard to get a notification from SmartThings because it is cloud dependent for all notifications.
So you might just want to consider a commercial freezer alert instead. But of course it depends on the value of the items that might be spoiled (either financial or reputational).
If you decide you do want to go ahead with SmartThings, there are lots of discussion threads in the forum from people who have done freezer monitoring with various different devices. You can just search on “freezer” Using the magnifying glass icon in the upper right of this page and you’ll find several of these.