I recently aquired no less than two Phillips Hue Tap Dial Switches and a lot of (non-smart) dimmable led light bulbs. That seems to have been a misstake as the Philips Hue Smart Plugs (suitable for swedish electrical sockets like the one in the picture) I use mostly only supports on and off.
Is there such a thing as a dimable smart plug that is working with HE7?
I think you'll find there are many dimmable smart plugs but they are of the 2 prong variety; I have many but not in use.
They will pass a small amount of current to the bulb to keep the electronics alive in the plug.
The downside is you will often have a small glow from the bulbs in a dark room with this trickle current.
I believe the only devices that need this trickle current are those with no neutral. Simple mains powered don't need a trickle current. Some devices may choose to monitor the load an use a small current to do so.
The Z-Wave+ devices I have are GoControl PD300EMZ5-1 from Nortek.
They dim but, as stated earlier, have a trickle current. I used to use them on my X-Mass tree lights but at night the strings were always very dimly lit when off.