If you're asking in the context of directly using the File > Import... command in VMware Fusion the answer is no.
If you're asking is there a way to create a Virtual Machine either using the USB Device itself as the Mass Storage Device or from the USB Device as a Virtual Hard Disk the answer is yes.
Why do you want to create a Virtual Machine from the USB Device? I'm asking so as to provide the better course of actions.
With that said it might actually be faster to create a Linux Virtual Machine using the Source ISO Image used to create the bootable Linux USB and then if needed/wanted to transfer specific User Data or other Files to the VM.
The easiest thing to do is to boot the USB Device connected to a Virtual Machine using the Plop Boot Manager. This would run the OS from the USB Device attached to an empty Linux Virtual Machine and thus everything after Plop chain loads Linux it all just happening from the USB Device. (I do this to update my KAV Rescue USB Linux.)
Another avenue is to use vmware-rawdiskCreator to create a meta-data .vmdk virtual hard disk and then either use it as is or then use vmware-vdiskmanager to create a normal file based .vmdk virtual hard disk, either of which could be added to an empty Linux Virtual Machine to run from. Note if using vmware-rawdiskCreator to create the meta-data .vmdk virtual hard disk to add to an empty Linux Virtual Machine it will need to be added manually, by editing the .vmx configuration file, as it will not be selectable walking thought the New Virtual Machine Assistant or the Virtual Machine Settings. On an additional note you may have to tweak the install when created directly from USB in this manner and why in the beginning I mentioned "With that said it might actually be faster to create a Linux Virtual Machine using the Source ISO Image used to create the bootable Linux USB and then if needed/wanted to transfer specific User Data or other Files to the VM.". A .vmkd virtual hard disk created byvmware-vdiskmanager can be added to the Virtual Machine either while walking through the New Virtual Machine Assistant or for the Virtual Machine's Settings.
vmware-rawdiskCreator and vmware-vdiskmanager at located at: "/Applications/VMware Fusion.app/Contents/Library"
In a Terminal, executing either without any argument outputs the internal help showing syntax, etc.
