Asher J. Klassen has the best only-time-to-read-one-SDCC-is-right-now piece up on the band Everclear making use of an artist's appropriation of Jaime Hernandez's amazing red and black Love and Rockets band image. It opens up that whole thing about homage versus appropriation, which is something that I think a) you have to feel your way through, b) it's not that hard to do that.
I'd say in this most reasonable standards would say the artist and those supporting the artist's action through pay and use are in the wrong. As Klassen points out, making an homage to fulfill a paid assignment is dicey territory. The fact you could reasonably look at this and not knowing which image came first not be able to tell kind of makes a lie that one image is a tribute paid the other. Eric Reynolds points out that the image was never part of a work for hire deal by which the artist would have ever not had the rights, which isn't an angle I've ever considered.
It would be nice if a proper poster were commissioned from Los Bros instead, although the problem with that is that Jaime Hernandez prefers working on his comics and may not want to take on that job, or work for those folks. I wouldn't. Maybe another solution would be to pay him for this one as if he had worked on it. Because he did.