ventilation using off ridge vents

I recently had a new metal roof put on over my previous shingles. I had off ridge vents on top of my roof with my shingles along with soffits at the bottom. The roofer did not cut new along the top of the roof for the ridge vents but rather placed metal over my off ridge vents. He did this because he believes that the heat will rise and come up the off metal ridge vents and go up the raised parts of the metal and out the top of the roof. Has anyone heard of using previous off ridge vents as a substitute for cutting along the entire top of the roof? I also have gable vents by the way. I just want to know if I will still have adequate ventilation in my home. Thanks.