Personally, I'm least concerned about the backup PG spot. While I was paranoid the past couple of years about Rondo's ability to handle the position full time, he clearly proved he can be a full time starter at this point. And with his athleticism and youth, he can certainly play big minutes. Thus, though I don't love House and Pruitt at the point, I could live with the two of them backing him up. While House doesn't run a team well, he can manage in the regular season and handle the whopping 5-10 mpg he'll actually get backing up Rondo in the playoffs.
So I'd certainly be open to Williams if he wants to come for the minimum. He probably has more to offer than Pruitt and probably can't be any worse as a 3rd stringer. And who knows, maybe he'll even beat House out.