I don't think tune up fights really exist in the UFC. Sure, he'd be favored against Anderson, but Anderson is more than capable of winning that fight.
I'm not sure a win over Anderson is enough to get a shot before Jan/Glover if they do that fight at roughly the same time. Since Santos lost to Jones, Jan would have wins over Rockhold, Jacare, Anderson, and then Glover. Glover would have wins over Krylov, Smith, and then Jan (plus wins over Cutelaba and Roberson before that). The UFC will of course do whatever they want, but it makes it more of a question IMO.
So basically, I think the risk/reward is not there for Santos to fight Anderson. If I was him, I'd rather get Glover or even a rematch with Jan in a true #1 contender fight to all but guarantee I was next in line. He'd be favored against both of those guys, too.