Hi @angryphd and thanks for your query. Whilst the Unreal Engine is not currently supported, you can still develop immersive virtual reality applications with eye tracking using our XR SDK built upon the Unity Engine.
To get started using with our Unity API under the Vive Eye Pro, please check out our getting started tutorial @ https://vr.tobii.com/sdk/develop/unity/getting-started/vive-pro-eye/
Hopefully, this can suit your project requirements. Please do let us know if we can provide additional support.