I’ve recently added Hue Sockets to the Hue without the Bridge App and Zooz Zen52 dual relay all via the Homey App. Unfortunately they both come up with Unknown Device and added as a generic device, the Hue socket is added as a dimmer switch which is usable but the ZEN52 only sees it as a single channel generic device.
I’ve removed and added them back (z-wave with no security), restarted the Homey but just can’t get it to recognise the devices, even though they are listed as being supported by the Homey App.
The smart plugs likely use another Product ID (other hardware revision) that’s not yet supported by the Philips Hue without the bridge). I would recommend to use the Hue Bridge (you can get them second hand for €10-€15) because it has support for firmware updates and official Homey support.