After some fiddling around I found out that my idea works as expected. There seems to be a bug in Parallels or maybe Windows or Mac OS X that occurs when you boot the VM and have the second HDD assigend to the VM as described above.
Summary / Steps to reproduce:
Requirement: A second HDD in your Mac that has one Mac OS X and one NTFS partition
1. Add an additional Hard Disk to the Bootcamp VM and assign it to the second HDD in your Mac
2. Boot the VM
3. In Finder you will see that the two partitions of our second HDD will disappear and only the Mac OS X partition will a appear again after few seconds
4. You can notice that you can't really access the Mac OS X partition on the HDD because it seems to be empty
5. In Disk Utility unmount and mount the Mac OS X partition on the second HDD
6. You can now access your Mac OS X partition on the second HDD
7. You also can now access the NTFS partition directly in your VM
(8. The NTFS partition is in access and can't be mounted in Mac OS)
Last edited: Nov 21, 2011