Probably these people if they knew they were going to work for Uber, they wouldn't have signed on. But Otto, sure, why not. Otto really was, at the face of it, a recruiting agency for Uber. (An expensive one, I'm sure..)
This case might be a little different given the short time this team existed though.
Considering that, IMO, Valley companies severely overestimate that risk I think acquihires are a really expensive way to acquire people.