Yep, I had a Linux VMware installation successfully using the external modem on my Win2k host. It works just like you think it would, basically. Just add the serial port to the guest OS configuration.
I've got a site with a VM-in-a-box setup on a single Dell R510. We're running some licensing VMs that need access to USB HASP keys only we've run out of available USB ports on the box. Does anyone ...