Butternut is closely related to walnut...in fact the botanical name of both starts with Juglans. Walnut is Juglans nigra and Butternut is Juglans cinerea. They both contain the juglone toxin.
Every part of the tree contains this chemical, including the roots which spread out much farther than the spread of the branches. So plants that are susceptible to this toxin will be affected further out from the tree than most people realize.
There are quite a few shrubs that do well around walnuts. If you check online there are some sites by Cooperative Extension agencies that list what plants do well around these trees.
Many vegetables do not do well, however.