"One thing I can't argue with is the Holy Spirit is convicting people to a saving knowledge of God through Warren's ministry."
I can.
It's not Rick Warren's doing. He's not convicting anyone with his lies and humanistic teachings.
When a person seeks HIM, He will be found. They would have found the Lord with or without Rick Warren. Rick Warren doesn't call the shots - God does.
Rick Warren is doing what he believes God is calling him to do, the Holy Spirit does the actual work. And if that happens through Warren's ministries then I'm going to rejoice the Body is growing through Warren's ministries.