Most people run both, and in fact that’s the only setup that’s officially supported by both companies. 
I ran both for about 5 years. The hue hub was much more stable than the SmartThings platform, so it served as a “plan B” for times when ST was being flaky, as it continued to work with Alexa, Apple HomeKit, and its own app.
FAQ: Do I need the Hue Bridge/Hub to Use a Hue Bulb with SmartThings?