Question: can orochimaru use sage mode?
Answer: Yes he does, Orochimaru CAN use Sage Mode. More particularly, Snake (Dragon) Sage Mode. That's how he learned all the snake-thing jutsus, just like Jiraiya with toad-ish jutsus of him. But that was before he started to use his immortality jutsu, his immortality jutsu required him to take over one's body.