It makes it more difficult. Regardless of how many accounts he has, he would have to have the SP to vote in 20 witnesses. The rest of the participants would also be able to vote.
For example:Let's say he has 20 SP and you and I have 1.1 each. He could vote in 20 witnesses, but you and I could vote in our own witnesses each. It is harder for him to create a consensus by himself. It wouldn't make a difference if his SP was split among 20 accounts or 1.