Hi Intrepidity,
You can setup a crontab for ESXi, unfortunately it's not as straight forward as it would be on an ESX or any UNIX/Linux host using "crontab". Having set that, there are a few solutions and it depends on how your environmental is setup.
Here are a few posts on some solutions that have worked or recommendations.
http://communities.vmware.com/message/1107603#1107603
http://communities.vmware.com/message/1108641#1108641
http://communities.vmware.com/message/1108327#1108327
If you're looking for a centralize location to configure your backup entries, you can do using Windows Services for UNIX using the scheduling services as you've suggested, or use windows task scheduler and plink.
For UNIX/Linux solution, what you can do is have a centralize Administratrive LUN that is visible to set of ESX/ESXi Server(s) that you need to run backups against and store different set of configuration files based on backup schedules and the backup script itself:
(e.g)
host1_backup_weekly
vm1
vm2
vm3
vm4
host2_backup_daily
vm5
vm6
vm9
host3_backup_hourly
vm4
vm9
Then what you can do is schedule the backup schedules using a cronjob and relying on SSH keys, you can remotely connect from a UNIX/Linux system and execute the backup schedule based on these configuration files.
(example crontab entry)
#weekly backups
22 4 * * 0 ssh root@host1 "/vmfs/volumes/ADMIN_LUN/ghettoVCB.sh /vmfs/volumes/ADMIN_LUN/host1_backup_weekly"
#daily backups
02 4 * * * ssh root@host2 "/vmfs/volumes/ADMIN_LUN/ghettoVCB.sh /vmfs/volumes/ADMIN_LUN/host2_backup_daily"
#hourly backups
01 * * * * ssh root@host3 "/vmfs/volumes/ADMIN_LUN/ghettoVCB.sh /vmfs/volumes/ADMIN_LUN/host3_backup_hourly"
This again, relies on two keypoints:
1) ESX/ESXi seeing a common LUN to locate these backup files and the script itself, else this will not work.
2) SSH public/private keys are setup/enabled for this to work without having to prompt for a password when making the SSH connection
Sample Run:
This is a quick example that shows the execution of the backup script being executed off of our VIMA box to our remote ESX Server and having all it's configuration files/scripts located on our NFS LUN. This can be extended to as many hosts as you would like and configured to fit your environment.
[vi-admin@vima-primp-industries ~]$ ssh root@172.30.0.254 "/vmfs/volumes/kevin-test-nfs-storage/ghettoVCB.sh /vmfs/volumes/kevin-test-nfs-storage/simple_backup_file"
root@172.30.0.254's password:
################ Taking backup snapshot for RESNET-UCSB ... ################
Destination disk format: VMFS thick
Cloning disk '/vmfs/volumes/himalaya-local-SAS.VMStorage/RESNET-UCSB/RESNET-UCSB.vmdk'...
Clone: 100% done.
Removing snapshot from RESNET-UCSB ...
#################### Completed backup for RESNET-UCSB! ####################
Start time: Sun Nov 30 11:23:14 PST 2008
End time: Sun Nov 30 11:23:38 PST 2008
Duration : 24 Seconds
Completed backing up specified Virtual Machines!
Hopefully this helps answer some of your questions.