If you don't want to put the Hue Bridge in the middle, I believe they'll already work if you pair them directly to Hubitat (as regular Zigbee devices) and used the "Advanced Zigbee RGBW Bulb" driver, or possibly any community or built-in driver that otherwise meets your needs. This is one that I believe should because it does XY-to-HS color-model conversion.
It's theoretically possible to write a Hue Bridge integration that does, too. I've tried. The results weren't great. 
It's possible I'm using an unsuitable formula (or a wrong input, like the wrong white point, but everyone seems to use the same value for Hue here). I'll probably pick it up again sometime or see if Hubitat's conversion is part of their "public" libraries now and able to be used by third-party drivers (freeing me from most of that work!), though I can't guarantee it will behave differently/better. FWIW, Home Assistant's XY-to-HS conversion was similarly bad for me (I think I was able to even get the same values they did), but I don't think anything there necessarily depends on a specific color model since "capabilities" aren't quite as standardized as they are on Hubitat and you have more latitude with how things are set and reported, so your ability to use them less affected.
But it would be great if Ikea's firmware reported HS values out like most (actually all I've seen) other RGBW bulbs do...
