I don't see a way to do arbitrary rotation when I'm cropping. Is that a pending feature or am I missing something?
You are correct, its not possible to rotate the image during a crop operation. It is possible to rotate it first as a separate step, using the Move layer option along the top, the one which looks like a plus sign with arrows on the tips. When selecting this tool there is an option on the righthand side for rotating the layer, icon is an arrow circling in on itself. There is also an option in the menu (expand the menu to see it) at the bottom below the Cancel and Done buttons to enter a rotation value numerically. After you rotate it, then you would just crop it as a second step.
You could create a idea thread as a feature request to have it added to the crop command. The development team reviews these and considers them when making updates to the product.