Before much reliability was available in Holstin bulls for calving ease, it was a fairly common cross. Just as using an Angus bull on Holstein heifers was. Using a Hereford on a Holstein you will get a much more traditionally marked black Hereford looking calf, i.e. white feet, neck patch, etc.
Having used this cross in a cow herd many years ago, here's what we found. The calves don;t narket as well as straight beef, the bulls market better then straight Holsteins, but the heifers market much worse then Holstein heifers. It takes some pretty exceptional pasture or a lot of grain to keep these girls in decent condition and they milk way more then is needed. We used to have them raise 4 calves at a time. The next generation using a beef bull will start to mitigate the milk some, and the current dock for poor muscleing starts to be less significant. As gro9wn cows they bring about the same money as straight Holsteins for killer prices. If you need more milk in Herefords, there are some high milking Herefords available that won't contribute the problems of using Holsteins.
Around here they're referred to as "Hillbilly Highbreds".
dun