@nibzy26
Just to add a bit more clarification.
You need the official ROM because of the Vendor Specific Propitiatory Code or the vendor blobs as we call it , This blobs are located in the vendor partition of your device and are installed with the official ROM , UT cannot take this blobs and distribute them because this violates some license (Not very familiar what exactly) so thats why they need to be preinstalled on your device and thats done by the Official ROM (because they are distributed with it), when you flash UT on your device it does NOT delete this vendor partition (vendor blobs) but instead Halium is using it in order to make UT communicate with the hardware. Hope thats clarifies to you why you need Stock ROM installed on the device before installing UT.