By default there is no SSH capabilities enabled by ESXi server as the console is locked down by default. However, VMware conveniently allowed a limited backdoor that can be enabled via the Remote CLI or on the console of the box if you have access. You basically once you have logged into the service console enable the following options:

• Enable Local Tech Support
• Enable Remote Tech Support (SSH)
• Modify Tech Support Timeout

For more information, please reference the following link below:
http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1017910