Nobody REQUIRES anything, at least not yet. It is a good idea, however, to be tested for genetically passed illnesses, and Dor Yesharim is a great way to do so. HOWEVER, they do not test for everything, and sometimes genes that could be problematic are missed. I have a friend whose child has a baby with a non-life-threatening condition but one which will always cause the child a problem,, and there is a 25% chance of it being passed down to every child they will have. Totally unknown to them, the mother and the father each had a gene that causes a certain condition, but it would never have been tested for its presence, and is definitely not tested for by D”Y, though I think it should be, as they test for so many other things.
I don’t know if D”Y should be called every time a shidduch is proposed, but it should surely be checked up after the first date, if the couple wants to go to a second one. Not everyone is tested by D”Y, or needs to be, but I personally think it is a good idea.