Use of Deposition by Adversary
At trial, a deposition is subject to the rules of evidence, and evidentiary objections may be made, except for those that are waived by not being raised at the deposition.
Furthermore, the deposition may be used affirmatively when the deponent was an adverse party or an officer, director, or managing agent of an adverse party, or a person designated by the adverse party/organization to be deposed.
There is no requirement that the adverse party be unavailable to testify. (That is a requirement for using the deposition of a nonparty.) No exceptional circumstances need exist; that is more of a catch-all basis for using a deposition.