The Phillips hue bulbs originally use the ZLL (Zigbee light link) profile. They use this profile to communicate with the Hue bridge, which in turn can communicate with a SmartThings hub over the local area network. In this setup the hub does not speak directly to the bulbs. This is the only setup which is officially supported by SmartThings.
Most brands of zigbee bulbs can be individually reset through a “blink method” where you power the bulb on and off in a specific pattern, and then it will reset itself. Phillips chose not to offer that for their smart bulbs, perhaps because they were concerned about children playing with the light switch and accidentally resetting a bulb to factory specifications.
SmartThings does not use the ZLL profile. Instead, it uses the ZHA ( zigbee home automation) profile. Most ZLL devices, including the hue bulbs, can be paired to a ZHA coordinator like SmartThings and will then use the ZHA profile instead.
The problem comes when you decide you want to take that Hue Bulb off the SmartThings network and move it to a different one. Or reattach it to a hue bridge.
Because the hue bulbs cannot be individually reset on their own, you can end up with a situation where there is no way to move the bulb off of SmartThings without buying an additional device. (In the US, this is most commonly a Lutron connected bulb remote, $30 at Home Depot. Although it’s a different brand, it just happens to use exactly the right commands to reset A ZHA bulb.)
So this is why SmartThings support only recommends using the Hue bridge. Otherwise customers could end up with a bulb that they cannot move back from the SmartThings hub to a Phillips bridge, and Phillips would tell them that it was smartthings’ fault. 
But as long as you’re willing to buy the additional device if you do want to move bulbs off of smartthings again, it will work fine. As long as you have selected an appropriate device handler.
We’ll pause briefly here so that those who have not previously worked with custom device handlers in SmartThings can read the following FAQ and catch up:
[OBSOLETE] FAQ: An Overview of Using Custom Code in SmartThings (SmartThings Classic, Groovy Code)
So, the officially supported way to use Hue bulbs with SmartThings is to have those bulbs controlled by a hue bridge. You then add that bridge to smartthings, and the setup wizard for it will automatically add device handlers for the individual bulbs that the bridge tells SmartThings about. Which means the official device handler for Hue bulbs assumes that there is also a Hue bridge in the picture.
If you want to add a Hue bulb directly to the SmartThings hub without a Hue bridge, you can, but you will need to use a different device handler, which recognizes that the bulb is not attached to a bridge. It is likely that there will be different ones for RGBW bulbs and plain white bulbs.
It’s possible you could just use a generic zigbee dimmer device handler type, I don’t know if anything extra is needed.