Yes, it is possible to supervise the iOS devices without a DEP account.
You can supervise the devices using Apple Configurator 2. The iOS device should have OS version 6 or above to enable supervision.
Following are the steps for device supervision
1. Create a Wi-Fi profile.
2. Create Blueprint and add a Wi-Fi profile.
3. Prepare the device.
Please use the help link for a detailed explanation of the same.