When you take a snapshot of a virtual machine (for backup reasons), it might be that DataMiner is busy writing to the Cassandra or Elastic DB at that time.
Is there a risk of corrupting the DB when you'd restore that snapshot? If so, what'd be the advised way of taking snapshots?
Snapshots are not the backups. There is a possibility of the DB corruptions based on the timing, but you need to follow the best practices recommended by VMWare Overview of virtual machine snapshots in vSphere (1015180) (vmware.com) .
You need to develop a mechanism of the Disk backups and also Database backup's to make sure that you can recover the data to a particular point in the past.
Yes, there is a small risk of corrupting the DB with the snapshots but this is about how you manage the VMWare deployments. Snapshots are only for the purpose of recovering the complete system in case of unexpected scenarios.