Why not? Lots of people are upset that Nancy Pelosi and Robert Byrd want to do this, but I'm not sure I buy their arguments. Ted Kennedy wanted to to pass a major health-care reform bill. He called it the cause of his life. It's not as if renaming the bill would be contrary to his wishes or in some sense ironic. (Like, perhaps, renaming a gigantic public airport after a man who fired thousands of air traffic controllers and favored limited government more broadly.)
The legislative eulogizing might (or might not!) make the bill more likely to pass, and the intentions of the legislators might (or might not!) be a mix of the genuinely commemorative ("he would have wanted it") and the disingenuously opportunistic ("we want it"). But there should be nothing surprising or unseemly about a legislator motivated by a heartfelt belief that the best way of honoring Kennedy would be to pass a bill for which the man struggled. And the political effects of a heartfelt Kennedy commemoration are no more or less "fair" than the political effects of a 9/11 commemoration or Ronald Reagan's death in the summer or 2004.
On the other hand, I do have some sympathy for Jonah Goldberg's argument that the left can't have this both ways: It shouldn't expect to mobilize Kennedy's memory for health-care reform while maumauing Kennedy's posthumous critics. But this is mostly because I don't think we should have a general principle against posthumous honesty. If Goldberg has a moral principle that discourages such criticism (and he seems to), he should surely uphold that principle and hold his tongue no matter what the left does.