One would think Sands' roster spot is still shaky unless he beats out Stubbs (or Marchan does, though I think they want him playing everyday). They might be hoping to sneak him through, or they figure there's bound to be a 60-day spot opening before the season starts (though if that's a pitcher they probably need to give that to another pitcher). He also just might have been insurance until everything - the major league back-up job, trade talks involving either catching prospect - plays out. Which at this point it has (i.e. they did not make a major trade) but it's not all over yet.
By August 1 presumably Marchan will either be the major league back-up or with another organization, and O'Hoppe will have gone from AA to AAA. At that point either Stubbs or Sands could still be in AAA, or not.