I have a zigbee inline dimmer connected to a light over my pool table. https://www.amazon.com/gp/product/B07GSK1HVP/ref=ppx_yo_dt_b_asin_title_o00_s01
Connected to ST and it works great, however I’d like to have a wireless dimmer (something like the hue dimmer switch) connected to control it.
I’m wondering if anyone makes a device that can wirelessly control another dimmer, sort of like a wireless add on in a 3-way.
Sure, just don’t connect it to the same circuit branch. Treat the inline dimmer like a smart bulb, let it control how much power it draws.
Then have a separate switch that does not control the load. That switch sends a message to the hub, the hub sends a message to the inline device. 
You didn’t say which country you are in, and the device selection does vary, but you should have several choices. (The topic title is a clickable link) See the following FAQ: