Backup Exec is designed to take a new snapshot (using the VMware snapshot mechanism not ours) of the current state of a VM and then backup that newly created snapshot, we cannot hook into existing snapshots, which doesn't really meet your use - in fact most backup products that protect VMware VMs probably work in a similar way so not really sure you will find a good solution to achieve what you want. You kind of need a Disaster Recovery product for VMware itself that will also backup the configs and datastore content, and not a product designed to backup VMs (I have no idea if such a product exists)
In fact the way you are using VMware is not recommended as maintaining lots of snapshots can affect performance. OK training environments don't usually worry too much about performance, but products designed to protect business data don't usually get designed for or tested against test and training environments that use unique concepts only as a way of making training more efficient.
The usual way to reset a VM to a known good state is to use templates and re-provision from the template, however if you are trying to maintain a sequence of known good states for a single VM then that won't help you very much
What you could do with Backup Exec is
1) Backup to disk instead of tape as restores are faster (and you can then also use a function called instant recovery (but not for 2800 VMs at the same time)
2) Backup the VM it its initial state as a full backup
3) Make your desired changes for 2nd state of the VM and then back that up as an Incremental backup
4) Repeat step 3 for the 3rd state etc
You will then be able to chose which state to restore as a point in time from any one of the full or incremental sets. You will also be able to redirect to give the VM a different name, which might mean if all students use the same image you only need one set of backups of the stages of the VM itself. (although note the actual hostname inside the VM is not changed when redirecting a restore).
BUT this method will never allow you to recreate the snapshot sequence (as restoring an incremental would just create a VM with no snapshots but matching the point in time of the incremental) The only way to recreate the snapshot functionality would be only restore the full and then get an admin to work through the stages making a new snapshot as they reach each stage.