Most believe the Oakland Raiders could use an improvement on the offensive line. That is to say, the Raiders could stand to get better at three positions on said offensive line. That's a whole lot to potentially improve upon, especially when you're lacking a first round pick. The 49ers had similar needs a year ago, but they possessed two first round picks, and spent them accordingly. It's unlikely that the team can get three starters on the offensive line when their highest pick is mid-second round, especially with the question marks elsewhere.
They have significant needs at the very least at one tackle and one guard position. A lot of people might say they have a need at center as well, something the folks over at Silver And Black Pride took a look at recently. Samson Satele is currently that guy. Their poll results indicate that most people believe him to be "good" (47%) or "average" (43%). Personally, I'm in the camp that considers him "good," and thus, I don't think the Raiders need to be drafting a center high.
The problem with that is that Satele is a free agent, though we don't know what even means at this point. Still, it's something to consider. If somebody falls in the draft, do the Raiders then draft them? Still doubtful, considering their other needs. Assuming they are able to keep Satele and you are one of the folks who voted "bad" or "terrible", you're thinking the Raiders should be drafting a guy who can step up and take the job from him.
It's just not likely to happen at this point. The best center in the draft, Stefen Wisniewski, will be gone by the time the Raiders draft. After him, there's nobody who can come in and start right away. Short of trading up and losing their already lacking draft picks and ignoring other key needs, the Raiders will be starting somebody who was on the roster last year or a free agent.
As the article linked above states, that's not necessarily a bad thing. Satele is, at his worst, average. He's capable.