Short Answer
Not necessarily. Modern architectural shingles can have construction and thickness characteristics that make them inappropriate for use as ridge caps. Purpose-designed ridge-cap products should be used when required by the system.
Detailed Explanation
In the past, with 3-tab shingles, it was common practice to cut shingles into ridge caps. But modern architectural (dimensional) shingles are thicker, have a different construction, and are not designed to be bent and installed at ridge and hip lines. Cutting them for ridge use can result in improper sealing, reduced wind resistance, and warranty issues. Manufacturer installation instructions typically specify purpose-designed ridge cap products for their architectural shingle lines. Using cut field shingles instead can void warranty coverage and compromise performance at the most wind-vulnerable part of the roof.
Why It Matters
Using cut shingles instead of purpose-designed ridge caps can void the manufacturer warranty and compromise wind resistance at the roof's highest point.
Code & Manufacturer Considerations
Manufacturer installation instructions specify acceptable ridge cap products. Using non-compliant materials may void the manufacturer warranty.
Building codes and permit requirements can change. Always verify the current requirements applicable to your municipality and project.