I am just going back through my old emails and found a few that 'fell through the cracks' so to speak. OVZ is quite a different technology to other VM type scenarios and I have not used removable drives with it before so I can't offer a lot of guidance. I have had experience forwarding internal drives/folders to OVZ containers (under Proxmox) and had it working very successfully but I'm not sure how great that'd be for removable type storage (I mounted the folder with the OVZ container turned off and then booted it up - and leave it connected all the time). And as by default PVE doesn't automount external devices you'll need to manually do that for starters (or configure it to automount - PVE is based on Debian so shouldn't be too hard).

So rambling aside, bottom line is that this is a question probably best asked over on the Proxmox forums, although the OVZ forums may also provide some insights. Actually, maybe a good idea to search the forums and the relevant wikis first... (PVE wiki, OVZ wiki).