Yes you can.
So presumably a Shared Review started with Acrobat 9 could also be responded to with Reader X? I have such a user that can't seem to connect to the review, though he can open the document.
If the review has been initiated by Acrobat Professional or Acrobat Professional Extended, then this review can be acessed by Reader users. However if this review has been initiated by Acrobat Standard then Reader users will not be able to connect to the review.