> Rivian’s marketing people probably hate that they’re doing this

Somehow I doubt it. It's a big payday for the company and a big vote of confidence by a customer that doesn't mess around (as far as practical concerns go, ethics obviously doubtful). If Rivian wants to sell practical work EVs, this is their ideal scenario. People actually in the market for EV vans are going to do the math, and mostly won't care about the vague contamination by association with the Amazon brand.