No, the doctrines of grace should not be hidden. We need to understand, however, that they are not the gospel in and of themselves but describe how the gospel works.
Jesus preached sovereign grace to thousands of unconverted people. He did it in John 6 and John 8. He also preached it in John 10: “I lay down My life for the sheep” (John 10:15), and His audience was the Pharisees. On the day of Pentecost, Peter preached the doctrines of grace, specifically the predetermined plan and foreknowledge of God—“As many as the Lord our God will call to Himself” (Acts 2:39). Following the pattern and example of Scripture, we should not withhold these doctrines from unconverted people. There have been times when I’ve even preached on the doctrine of reprobation and double predestination, and unbelievers have been converted.
Every witnessing situation is unique. When you read Matthew, Mark, Luke, and John, the manner in which Jesus addressed the woman at the well was different from Nicodemus, or the scribe, or the rich young ruler. There is a different approach angle concerning the one true gospel in different situations and with different people. It may prove wise to use the doctrines of grace if the person is proud and arrogant and thinks that they are in control of their own destiny. I would not deny that at all, especially given the example of Jesus, who played hardball with the Pharisees. He was gracious, kind, and patient with everyday people. However, with the leaders who were stiff-necked and uncircumcised of heart, Jesus brought out the stronger doctrines of sovereign election and effectual calling, even going so far as to say, “The reason you don’t believe is that you’re not one of My sheep” (John 10:26). That is a pretty strong use of the doctrines of grace with an unbeliever.
J.C. Ryle said that it takes a whole Bible to make a whole Christian, and I think it takes a whole Bible to even be effective in evangelism. So, I would not hold back any truth if I felt at that moment that it would be wise and prudent to use it. I do not think any doctrine is off the table in an evangelistic situation.