May married men be ordained deacons?
Yes. The Second Vatican Council decreed that the diaconate, when it was restored as a permanent order in the hierarchy, could be opened to "mature married men," later clarified to mean men over the age of 35. This is in keeping with the ancient tradition of the Church, in which married men were ordained into ministry.
Also in keeping with ancient practice is the expectation that while a married man may be ordained, an ordained man, if his wife should die, may not marry again without special permission.
"Celibacy Affects Every Deacon:
In one way or another, celibacy affects every deacon, married or unmarried.
Understanding the nature of celibacy—its value and its practice—are essential to the married deacon.
Not only does this understanding strengthen and nurture his own commitment to marital chastity, but it also helps to prepare him for the possibility of living celibate chastity should his wife predecease him. This concern is particularly unique within the diaconate.
Tragically, some deacons who were married at the time of ordination only begin to face the issues involved with celibacy upon the death of their wives. As difficult as this process is, all deacons need to appreciate the impact celibacy can have on their lives and ministry." -- National Directory for the Formation, Ministry, and Life of Permanent Deacons in the United States, par. 72."