OK, got this working now. Quite simple when you know how
If anyone wants to do this in the future, this is how its done:
Firstly download the VMware images from the Meteohub web site and expand the archive.
Then download the VMware Converter program from the VMware site.
Convert the Meteohub VM into a installed VM on the ESXi host using the converter program, but don't select the automatic power on option. Also make sure the disk format is "thick".
If you are using the free 5.x licence for ESXi, make sure the VM version is set to 8 or below.
Edit the new VM settings to set USB (or serial) passthrough to connect the weather station to the new Meteohub VM.
Start the new VM and enjoy
The VM Converter program seems quite resource heavy - it quoted over 14 hours on my i7 laptop
I just spun up a new Windows 7 VM with 8 cores and 16gb ram and it completed the conversion in 5 minutes...
Had a play and it seems a great program and I really like it but unfortunately it doesn't upload regular webcam images to Wunderground, so the hunt for software continues