According to this new KB article there’s a backdoor for ESX3i:

  1. Log in to your ESX Server 3i at the console.
  2. Press Alt+F1 to switch to the console window.
  3. Enter unsupported to start the Tech Support Mode login process. Note that no text will appear on the console window.
  4. Enter the password for the root user. Tech Support Mode is now active.
  5. Complete tasks in Tech Support Mode.
  6. Enter the command exit to exit Tech Support Mode.
  7. Press Alt+F2 to return the server to DCUI mode.

For more info check the KB article. I will be checking out this feature over the next couple of days to see what’s possible in this mode.