Facts are not the friends of the right wingers. Here is the reality: 2013 was the fifth year that President Obama and his family held a seder in the White House. And Obama was not the first president to do so; the Clintons held seders during their time in the White House. If any earlier president held a seder in the White House, I couldn't find a record of it, but my search was by no means exhaustive.
Hammer appears to be a comedian mocking the Tea Party paranoia that Obama is a Muslim; but it is apt, it is consistent with the kind of thinking we have seen expressed repeatedly by the right. It's an appropriate post for April Fool's day, because that kind of thinking - the paranoia, the conspiracy theories, the absence or willful ignorance of facts are all characteristic of fools.
I have to admit that there is something pretty funny in Christians attacking a Christian for being a Muslim who holds a passover celebration in the White House to be inclusive.
Can you imagine how many heads would explode on the right, figuratively speaking, if as an indication of that religious inclusiveness, Obama recognized the important religious holidays for other religions - like Islam, Buddhism, or for Sikhs and Hindus? I wish he would have a dinner dedicated to atheists.
If I have any problem with celebrating a religious holiday in the White House, it is that we aren't inclusive enough, that we should not limit them to Christian and Jewish events.