Sure. What do you think about Kickstarter's liability in this in terms of their allowing these projects when their rules clearly state projects musty have the rights to the I.P.? They can't claim they were ignorant of this.
If I was Peters's attorney, I'd be impleading them. But the thing of it is, win or lose, he'd be burning the bridge there, big time, and would probably find he suddenly could no longer crowdfund, anywhere (even at GoFundMe or Patreon or any another place where he has not yet tried to get $$). So you do a cost-benefit analysis. Better to implead them now, or gamble that you can use 'em for crowdfunding later?
I'd advise to implead them now, as this is the more immediate issue, and future crowdfunding is a much more dubious thing.