That is correct. The ST hub would be controlling it.
If you ever wanted to switch back to the hue bridge, you simply reset it and add it back to hue.
Yes, you can program it several ways. Set it up to operate basically like it is on the hue bridge or you can configure up to 4 separate buttons with two commands each. For example, I set a simple press on button #1 to turn on a light and a long press on button #1 to turn off that light. I set another button with simple press to open all my shades and a long press to close them.
I switched my hue dimmer over last week and so far, I am liking it.
Note: I should amend to correct one item… when connected to the hue bridge, you could set up to five actions on the 1st button (on) for the lights you selected whether dimming levels, etc so you can’t duplicate that part…on ST… there are only two commands for each of the 4 buttons.