Hatch lines in Pages

It won't be fun and is guaranteed to be tedious. The end result cannot apparently be added to your custom shapes library but can be selected, copied to the clipboard, activates Previews New from Clipboard, and becomes available in Preview as a PNG image. If you want a vector object for Pages v13.1 or later, you can create the artwork in the free Inkscape and save it as an SVG image.

1. On the Pages Settings : Rulers panel, select all of the Alignment Guides options. These will dynamically appear for the following steps.
2. Insert a rectangular shape and set it's Style to No Fill. That gives you a transparent background shape.
   1. Set the line thickness and color as preferred.
   2. In the Arrange panel, set the dimensions of your box to exactly what you need.
   3. In the Arrange panel, set Text Wrap to None so you have freedom of movement with this shape.
3. Insert a line shape from the Style panel, and set its color then thickness to match the rectangle.
   1. From the Arrange panel, set its height identical to your rectangle height.
   2. Set its Text Wrap to None for the same reasons as the preceding rectangle.
   3. Press the option key and drag (duplicate) the line shape to the right at an appropriate distance for your line shape design separation.
   4. From the Arrange panel, group the first two lines.
   5. With the first two line group, press the option key and drag to the right to form the next set of lines.
      1. You will observe that as you duplicate and drag to the right the line groups, dynamic alignment guides appear to guide you.
      2. Repeat while the array of lines fits within the rectangle and then drag the lines group over the rectangle. You may need to increase or decrease the height of the lines group to deal with any bleeding outside of the rectangle. With just the lines group selected, and using the Arrange panel, force the lines group behind the rectangle.
      3. Select all and group.
   6. Finish the corner lines in the rectangle with separate short line segments and group these to the existing rectangle and line group.

Would using an isomorphic approach with transparency and separate shapes help such as in this example from a Pages document I did awhile back?

Otherwise you will need to show what you mean by hatchlines in the context of what you are attempting to do.

Or this using a texture pattern from SubtlePatterns:

or this: