Doesn't Mike Mangini play Zildjian sticks but use Vater Cymbal Toppers
I don't know what he uses, but those are different
products, so there's not an issue of exclusivity.
But funny you should mention Vater...
Before they were "toppers", Samson Fastener manufactured/marketed them as Slicknuts, and I endorsed them. But when Vater took over distribution and put their name on them, I dropped the endorsement because I felt it was a conflict to use Vic Firth sticks, and a product bearing their competitor's name. It probably wasn't an issue for the companies involved, but my sense of integrity got the best of me.
However, there are a few instances where there's some cross-pollenation. Two years ago, when Zildjian bought Vic Firth, and D'addario (Evans et al) bought Pro Mark, endorsers of related companies were questioning how things would pan out. A Pro Mark and Remo endorser now fnds himself associated with Remo's competitor. A Vic Firth and Evans endorser finds his head company now owns the competing stick company. And in my case as a Sabian, Vic Firth and Evans endorser, there's now a connection to Zildjian and Pro Mark.
But, there hasn't been any weirdness from the involved companies... Vic Firth isn't trying to get me to switch to (their parent) Zildjian, and Evans isn't trying to get me to switch to Pro Mark. And because the sticks don't bear the parent companies names ("Pro Mark by D'addario" or "Vic Firth by Zildjian"...) there's no conflict.
Bermuda