Hi scriffles
Which hardware version of your VM you are working on, which kind of Linux you selected when creating this VM and which kind of USB controller/device you are trying to add to the VM? As there's significant changes between vS5.1 and vS6.7 it's hard to tell which change made the differences on VM settings behavior. As in age of vS5.1 we were still using C# client to handle host/VM operations but switched to host client or NGC in vS6.7.
Anyway, currently in vS6.7, USB2.0 controller is not supported to be 'hot plug/unplug' when VM is powered on. But for XHCI(USB3.0) controller and USB3.0 devices -- either host connected or from your desktop -- support to be added when VM is powered on. BTW, you don't need to have the VMware tools installed for this kind operation.