It's definitely a ring, and it's definitely indented. I've even crimped through the plating into the bullet beneath. I try not to, but depending on variances in brass thickness and nickel plating of my .357 brass, sometimes I can't avoid it.
Something that also helps is if the manufacturer resizes the bullets after the copper plating process.
Berry's bullets are indeed swaged, then plated, and resized once again.
Just for grins, I ran a batch of their plated .358" bullets through my Lee sizing die, and they were right on. That helps a lot for uniform crimp.
If I get a chance, I'll pull a bullet from my .357 Desert Eagle loads and take a picture.
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SOME of the berrys are double struck,(meaning swaged, copper plated, then sized again), not all of them. Unless they have changed to double striking all of them, they only DS a few. The raniers have the thinnest plating of the three most often talked about, berrys are thicker and west coast,(now called accura bullets), have the thickest. Accura also double strikes ALL their bullets.
http://www.accurabullets.com/ I've never tried to push plated bullets up to what you could expect from a jacketed bullet. I would think that the accura bullet would be okay up to what a jacketed bullet would do.