FYI: Here's a Mate 9 charging dock that works

Does it support fast charge when docked, using the OEM cable and charger?

You can't. It's a fixed cord.

I'm wouldn't even try if I could. I don't want anything in between my phone and that charger other than the OEM cable. Too risky in my book given the high power of that supercharger.
 
I have that unit, only one on Amazon. Just standard slow charge.

I test Apple USBC cables +MacBook uses a USBC and 65w charger) with OEM charger and would not deliver faster charging. Blackberry DTEK60 uses USBC but it's adapter and cable also would not. Only the Huawei set would.