I just followed jkopp's advisory about changing th vhardware version in thread ESXi 5.5 Free Hypervisor Web Console .
I just switched to v9 and was able to add my host USB HDD to the guest, so if you have the same problem as myself, just switch to HW version 9 and then you are able to connect host connected USB devices!
I do run the latest hardware version on all of my VM's and I have exactly the same problem. Any other ideas that I can try? Im able to mount the HDD on ESXi but can't seem to get them on my Windows guest OS's.
Thanks in advance