Is it possible to login to a linux guest from the ESXi console - not via tcp stack, like zlogin in solaris global zone to a non-global zone?
I don't believe so.
VMware always gives guests a graphical console, and I've never seen a menu option for it.
XEN just added VGA passthrough to XEN 4.0, and you could always do this with linux guests using the text console.
Although I'm sure it's possible to do this with just the ESXi console, you probably shouldn't because it's easy enough to redirect virtual serial ports between two VMs. Just have VMWare add a named pipe serial port to your virtual machine and then configure Linux to use it as a serial console. You then plumb that serial port to another serial port in the second VM running Windows + HyperTerminal (or Linux + minicom, etc) and you're done.
If you were looking to deploy this across a fleet of virtual machines or have it survive a vMotion event, you'd need to setup a Virtual Serial Port Concentrator (vSPC) which acts a proxy between your VM and the serial client. There are a handful of commercial products or you could try the open source vSPC.py.