Control Philips Hue lamps with IKEA tradfri Gateway?

Is this possible without the Hue Bridge?

Yep, it is. I have the same constellation running and it’s working as expected, also light colours can be set (however using the IKEA app only with specific colours). And I’m not yet sure about firmware updates of the hue lights…

Pairing is as with the IKEA lights, so you need a remote