I went to a Chargers vs. Raiders game up in Oakland in 2002 (the year we won in OT) with my brother and our cousin who is a Raiders fan. It wasn't too bad at first, because we were with a Raiders fan who kept telling his fellow fans to be cool, but I could tell that if it weren't for him, we would have gotten a steady ration of **** the entire game. As it was, we had two drunks hurling a non-stop string of expletives towards us, especially after the Bolts won. It wasn't a comfortable situation, but I can't say we ever felt threatened. However, I did see two fights between Chargers and Raiders fans, not to mention several between Raiders fans and Raiders fans. Those people are...different.
Of course, the Bolts fans and Raiders fans have a longstanding animosity, so maybe it won't be so bad for the Boys fans. But it definitely is not like visiting San Diego, where the fans are generally cool, if not particularly happy to see you there. The Raiders fans were definitely hostile.