To paraphrase Forrest Gump, "factory ammo's like a box 'o chocolates, you never know what you're gonna get."
The primers are most likely Federal 215s. These were developed specifically for the Weatherby cartridges, and they're the most likely candidates. Being nickle plated or left in plain brass doesn't really tell you anything, since the primers were probably run as an OEM item, and not subject to the same protocols as what Federal sells in their own boxes. If they're not Federal 215s, I can be pretty comfortable that they've been developed and tested to being completely compatable with the 215s performance. Don't sweat it, it's not an issue.