Doing this is asking for trouble, sort of like that time when the GOP tasked Stephen Colbert with M.C. some GOP event, apparently unaware of the "joke" that Colbert played the ultra-conservative on his show and was really a liberal.
That's not what happened. It wasn't a GOP event. It was a press association event to which Bush was invited.
Really, when you hire Seth MacFarlane to do ANYTHING you can't complain about what happens as a result.
When you hire anyone to do anything you have a right to complain if their work isn't the quality of what you paid for.
While I'm sure hiring SM was yet another attempt to 'appeal to younger viewers,' I suspect they producers hired him in large part due to his general wit and 'song and dance' /toastmaster personna. If MacFarlane can't tailor his act to the audience or the event that would would seem to be more a dig on his abilities than on the producers.