Id imagine a few people could get caught up in the moment.
To be fair though, I'd pay to see somebody wear one and stand right at the front at a Pearl Jam concert to see what the reaction is.
(Not much money though)
Now ask Pearl Jamm how much money that they have made off the back of Pearl Jam's music, image, logos, copyright infringement... I would wager it's relatively (very much) a one way street.
Looks like somebody (Pearl Jem) may have had a similar letter but didn't cry to the media about it. Doesn't look like they ripped off on the merch front either.
https://www.facebook.com/239070523876/posts/10158124729938877/
Is this down to Pearl Jam though? Or the surrounding suits?
EDIT: looking at this tribute band, they had it coming I'm afraid (imho and all that), they've pretty much infringed everything.
The fact its in a rehearsal room probably means it's hardly in the optimum state as it's likely to have 7 shades or stinky poo ragged out of it.
The fact that it is in a rehearsal room... and working should probably cement its status more than anything else.