The VEP seems to be policy rather than legislation. Meaning that there is no legal obligation for the US Government to abide by it.

If anything, the question is whether the US Government is morally obliged to reveal the vulnerability, given that the risk of not doing so is much higher than the value the government gets from exploiting it as a tool against terrorism. That, I believe, is the EFF's strategy – getting public support and appealing to the government's moral obligation to protect its people.