I’m using Xubuntu on several linux boxes and have seen missing icons in the VMware workstation GUI for several times now. This is annoying and makes every task a guess.
The reason lies in a missing index.theme file as mentioned in this VMware community thread [Missing index.theme]. I picked the file from the Tango theme and copied it to folders with the VMware workstations icons. This icon theme seems to support the naming schema best as stated in another VMware community thread [Icon Naming Schema].
Et voila. The icons are visible again.