IANAL but would love to hear what some more informed have to say about this. The law is constantly catching up to technology....
The point is what a designation is for; in the case of an arrest vs detention or seizure for natural persons, it's usually an elaborate shell game around when various search doctrines or other restraints on police behavior kick in. In the case of property, the only point is to grab your stuff; the circumstances surrounding it don't particularly matter because they can always decide later under one doctrine or another that they're entitled to keep it.
To make the question meaningful, I suppose you'd have to stipulate that the robot is somehow irreplaceable. Meaning it's the only one of its kind that's capable of representing itself as the body of Ed Snowden, and that it's the only means at his disposal for interacting with the outside world.
On the other hand, it's no stretch at all to say that the company who provided the robot is liable under US law for aiding and abetting him, especially if Snowden has to use their servers to communicate with it. (Well, OK, it's a stretch, but it's a stretch that the US judicial system has had no qualms about making in the past.) Our Federal courtrooms aren't often mistaken for philosophy classrooms.
It's not like those robots are only made for Snowden are they?
Those gas station corn dogs are a crime against humanity but a fine seems excessive.