First things first: The hue bridge has always used zigbee to communicate with its bulbs.
However, Zigbee allows for multiple “profiles” and these are not all interoperable. The hue bridge used to use just the “zigbee light link” profile (ZLL) and “zigbee green energy” for Its Tap Switch, but it did not use the “zigbee home automation” profile (ZHA). So bulbs which only used ZHA and did not use ZLL could not be connected to the hue bridge.
See the following FAQ (this is a clickable link)
What changed in February was that Phillips added the newest zigbee application profile, “zigbee 3.0” to the hue bridge. That in turn allowed more devices to be able to be added. But still not all zigbee devices.
To make matters even more complicated, the Osram/Sylvania bulbs use different Zigbee profiles in different regions. The bulbs sold in Europe use the ZLL profile, and can be added to the Hue bridge. The bulbs sold in the US use the ZHA profile and cannot be added to the hue bridge, even after the zigbee 3.0 update for the Bridge.
So unfortunately, you still will not be able to use your Osram bulbs with your hue bridge if you are in the US.
If you do have devices which can work with your Hue bridge, I personally would always recommend using them through the hue bridge because you can have problems with messages getting lost if you connect them directly to smartthings. See the following FAQ: