I have not heard of this.

(I have had tire dealers refuse to work on a car because I had a 3mm spacer.... 3 mm is the size of this: o

Technically, if they can come up with a reason that the spacer can be a cause, they can say the warranty will not cover it as the spacer is the cause of the claim. Changing the track can change the loading on the suspension and wheel bearing loads. Many will say "they must prove the mod caused the failure", but practically speaking, they can deny a claim with very slim rationale, and certainly not proof- and you are stuck trying to fight their decision.

You could always put the stock rims back on if there was a warranty situation relating to ride/suspension/etc