Osteen does preach a generic sinner’s prayer, for whatever that is worth.
His ministry doesn’t major in that area, however. He’s more interested in encouraging Christians in an area of exalting the Lord that many miss. I wouldn’t suggest that anybody try to live on a steady diet of just Osteen preaching. But it’s not clear to me that Osteen has the idea that you should, any more than a candy or ice cream store expects that candy or ice cream is all you will eat.
I don’t know if he knows the gospel, but he certainly doesn’t preach the gospel. And no man has ever been saved praying the sinner’s prayer. Many who prayed a sinner’s prayer are indeed saved, but they were saved by God’s grace, not because of their own prayers. Christians are “born not of blood, nor of the will of the flesh, nor of the will of man, but of God.” (John 1:13)
The Jesus Christ of Scriptures isn’t the weak Jesus men preach today. He’s not a begging savior who will come into your heart if you are willing. The Jesus Christ of Scripture is the King of Kings and Lord of Lords. He is ruling and reigning on His throne right now. Jesus Christ of the Bible was mighty to save to the uttermost. Those purposed to be saved in eternity past (Ephesians 1) will be saved. Every single one of them. ALL whom the Father giveth will come to Christ. (John 6:37)