It turns out that there is a solution for my problem:
Virtual Serial Port
VM-Ware allows to create virtual serial ports for the guest that are connected on host side to a named pipe.
I therefore created two helper programs, one on host side which listens on a TCP port and a specific named pipe and transfers all the incoming data between them.
A second helper program runs in the guest VM and does the same between the serial port and the TCP port I want to access.
The only draw-back is that the serial speed is limited to 128kBit/sec. May be that can be increased by using multiple virtual serial ports...
Virtual Machine Communication Interface (VMCI)
Using VMCI there is an API for creating a shared memory region that is accessible from both hast and guest system.