I have Workstation Pro 12.5.8 and a knowingly bootable (partitioned, successfully boots on a hardware machine) USB drive. All guest VMs recognize it with no problems if booted to Windows or Linux. But the BIOS of any VM doesn't recognize the drive, so I cannot boot a VM from the USB drive.
Some VMs are configured for USB 2.0, some others configured for USB 3.0. No difference. No difference if I power the VM on, then connect the device to the VM, and then issue Ctrl-Alt-Del, or power the VM off, then power it on, and it connects the device automatically.
As I press Esc, BIOS boot menu does not have the "+" sign before the "Removable devices" item. If I enter BIOS Setup and switch to the Boot tab, the "Removable devices" item does not have the "+" sign too.
I cannot use upgrade to 15.x because it has very poor real-time performance and I cannot get a real support from VMware at all.
How to force Workstation to recognize the drive?
The standard BIOS in the virtual machine does not support USB booting. Either switch the VM to use EFI BIOS, or use Plop Boot CD, boot into that, and it can load USB boot drivers.