I can't confirm that, there's plenty of plants around the regia tree in my garden. It has had fungus since forever (like every walnut tree I've ever seen), so that might keep it from doing that.
English walnut differs from black walnut in that the juglones -- the protective gas emitted by walnut trees -- are emitted less. Furthermore, it is easy to confuse water stress with juglone gas stress, so sometimes these symptoms can be remedied with more water.
Given what the parent commenter has said about having to experiment with different plants, it stands to reason that they have a healthy black walnut tree in their garden rather than a regia.
Given what the parent commenter has said about having to experiment with different plants, it stands to reason that they have a healthy black walnut tree in their garden rather than a regia.