In everyday usage het is often pronounced like ut. Next to that the last n in words like zeggen often is not pronounced very clearly. So there is not really a union, but these two things can make it sound like that.
You can listen to pronunciation examples of het here.
Jazzed and shushan2002 pronounce it like ut, orvowizard like het. Meranii pronounces it somewhere in between, which is not the most common way in standard Dutch.
At the beginning of a sentence, the "het" pronunciation is more common than somewhere in the middle or end of the sentence, where most people say "ut".
"Het regent" often sounds like "het regent", but "Regent het?" usually sounds like "regent ut?"
Neither is pronunciation is wrong, so you can pick your favorite :)