Can a congregation restore a person who was disfellowshipped by another congregation?
Members of a congregation withdraw their fellowship of someone in their midst who is living a sinful life. See Withdraw Yourselves for details. Membership in a congregation and the fellowship that ensues is done on a local level. No one can remove a person from the universal church except Christ. In actuality, a person loses his place in the universal church when he gives himself over to sin. When a local congregation disfellowships a person, they are merely acknowledging what has already taken place.
Each congregation is autonomous. The decisions made in one congregation do not affect another congregation. This can lead to some confusion when a person is withdrawn from by a congregation but he goes to another congregation. See Cross Congregational Fellowship for a detailed discussion of the problems that might arise and how they could be handled.
When a brother is restored, it means that he has left his sinful life and his brethren now recognize him as a faithful brother. "Sufficient for such a one is this punishment which was inflicted by the majority, so that on the contrary you should rather forgive and comfort him, otherwise such a one might be overwhelmed by excessive sorrow. Wherefore I urge you to reaffirm your love for him. For to this end also I wrote, so that I might put you to the test, whether you are obedient in all things" (II Corinthians 2:6-9). Whether a brother returns to Christ in one congregation or in another, it is a reason for rejoicing. It is a sin not to forgive someone who has repented of his sins (Matthew 6:14-15).