It is for both as the feature "host device passthrough" currently means pci and usb passthrough. Libvirt's virNodeDevice is used for device manipulation and "hostdev" XML element is used for the device itself.
Verified using build: rhevm-3.6.0.3-0.1.el6 (3.6.0-20)
Verification scenario:
1. Get host devices.
2. Get specific host device.
3. Post host devices to VM, run VM and verify devices are attached.
4. Get VM attached host devices.
5. Verify VM host device cannot be deleted when VM is running.
6. Power off VM and delete host devices.
Test plan added to external tracker.