S4c is funded by the BBC and advertising (I think ITV chuck in a few quid now and then too). I suspect they wouldn't be allowed to compete.
BTW, ITV didn't show a single Wales game in 2016 until the semi-finals. Of the 8 Wales games in 2 tournaments so far, ITV have shown 1.
So, on Sunday, I will be watching the S4C channel with the Radio Wales commentary - even though I have a huge hatred of BBC Radio Wales, it isn't as bad as ITV.