Hi,
there is thread regarding snapshot management on command line, it is for ESX 2 but the command should work anyway:
http://communities.vmware.com/thread/79237
Here is a detailed "man page":
...so just run the following commands:
To create a snapshot:
vmware-cmd <cfg> createsnapshot <snapshotName> <Comment>
To revert the last snapshot:
vmware-cmd <cfg> revertsnapshot
Anyway, here is the complete command line reference for ESX4, ESX4i and vCenter 4:
Cheers!
Max