Certificate is commonly used as a verb in the United States in education. I've personally heard and seen the phrase "certificated teachers" in California, Washington, and Texas. I've never seen the phrase "certified teachers" anywhere.

I think the usage may stem from the legal requirement for teachers to hold an actual certificate prior to being employed. I think it is different from "certified" in that no organization is attesting to anticipated performance, instead merely indicating that some past effort happened.

For example, a law school graduate is certificated, but not certified or licensed. They could go around claiming they are "certificated in law" without breaking the law.