It's tough to make the playoffs in the AFC, with basically every division being like the NFC East in competitiveness every year.
The Bengals, Jags, and Dolphins have crashed the playoff party in the last three years, so certainly, it wouldn't be impossible for the Raiders to do it, but:
1) The Bengals needed to go 6-0 in the division to make it last year
2) The Dolphins needed to get 11 wins to make the playoffs against a soft schedule, and couldn't have done it without Brady's injury
3) The Jaguars' starting QB threw 3 INTs in 13 games in 2007.
If you're into such stats, the
average team DVOA of these three teams was only 6.3%, or somewhere between the 2007 Redskins and the 2008 Redskins. So it's certainly possible. But as the Raiders have been the second worst team in football over the last three years, a playoff berth would require both a significant improvement (which is probably coming), and something terrible to happen to Philip Rivers, which may or may not be coming.