Most of the time the answer is yes it is harmful. Harmful because people who are entrepreneurs do not make good employees.

Entrepreneurs think differently than traditional employees. People who are entrepreneurs are the rock in their employers boot because they are always questioning "why" and "can't this be done better" . I am a business owner and once you are your own boss, working for someone else is very difficult. Most employers view it this way too. Most employers are going to assume and fear that you will be an extreme know-it-all pain in the ass.

You might want to say you worked FOR your company-leave it unsaid that you were the owner.