The Bible says that God will use anything to bring people into a relationship with Him. So, YES, martial arts can be a way to reach others for Christ.
Can martial arts and Christianity go together?

Iron Sharpens Iron
Daily Proverbs for Today's Martial Artist
This book is a devotional that will help you in your walk to develop the benefits of martial arts in your daily life. By looking at the teaching of Proverbs through the lens of a martial artist, you will see how the Bible is relevant and applicable to your martial arts training, understanding, and growth. Each day you will be guided to read a chapter of Proverbs followed by a devotion that highlights specific teachings within the chapter. The daily devotions are designed to strengthen your daily walk with Christ as you continue your journey of reaching mastery of your art.

Read an excerpt from the book...
Seek Knowledge
One of the reasons people start martial arts is to learn something new. They want to learn about the traditions, discipline, and the art itself. They come seeking knowledge about a new activity they can add to their life and, for some, to their family. No matter the reason, gaining knowledge is what helps us grow mentally, spiritually, and even professionally.