Auror or not, Severus was highly skilled in occlumency, and that wasn't going to change based on time period or location. He'd never given anything away before, and he'd stood up in front of the Dark Lord and lied to his face. A Longbottom in the greenhouse wasn't going to read him if he didn't wish it.
Then again, legilimency felt pretty unnecessary when Neville decided to go and fuck the concept of secrets by simply opening his mouth. Snape had to just stare at the other man for a long moment before pulling himself up to his full height, shoulders squared. "Have you some sort of information to share?" he countered, wondering really, what the point of denying a claim like that would do for him anyway, considering he was nearly twenty years behind.