No, it isn’t. I will leave the math to you, because the vote counts are public. The only states that Gore would have won if he got the votes from Nader were New Hampshire and Florida. New Hampshire only has four electoral votes. Sorry, New Hampshire, but you wouldn’t have been enough.
We all know that Florida was rigged, so that pretty much eliminates Nader as the root cause.
Besides, shouldn’t all of those Gore voters have voted for Nader anyway?