Can Ultron lift Thor's hammer?

No because the hammer has its power. Although Ultron has its power to make the hammer only a object than in hitting him could cause hurt. Ultrons power only makes the hammer be just like getting hit by a mortal getting hit with a hammer.

No because he's not worthy. He was trying to destroy the planet. If Vision can wield Mjolnir and he's the opposite of Ultron, there's no way Ultron is worthy.

Apparently nothing can lift the hammer unless it is "worthy", and that would include unliving objects like robots. If the hammer could have been moved, SHIELD would have probably used some sort of robotic device to collect it in the first "Thor" movie instead of building a compound around it in the desert.

But if you put it in an elevator...