An evangelist is a herald of the gospel, a preacher of good news. But he is not a pastor, or elder. An evangelist is a missionary. And being a missionary's wife no more makes a woman a missionary than being a pastor's wife makes a woman a pastor. God calls men to do his work and directs their wives to follow.
Missionaries are preachers.
If a man is not gifted of God to preach the gospel, no matter how sincere he is, he cannot serve as a missionary. And the message he preaches is, and must be, the gospel of God's free and sovereign grace in Christ, the sinner's Substitute. He is a man called and gifted of God to establish churches, train pastors, and help to establish those pastors and churches in the gospel of the grace of God, so that they might carry on the work of the gospel for generations to come. Missionaries are men sent forth into the world to preach the gospel of our Lord Jesus Christ, to gather in the harvest of God's elect scattered throughout the world.