I'm by no means an expert on the subject, but it has always seemed clear to me that priestly celibacy must be regarded as disciplinary and not dogmatic. It may be a discipline with a lot of tradition and theology behind it, so changing it would be a much bigger deal, but in no way can it be construed as dogmatic. If it could, the church would not be in union with Eastern Catholics who have a married priesthood, nor would married Anglicans, etc. be admissable into the Catholic priesthood.
I think a trickier quiestion might be whether celibate bishops is a dogma. All the ancient traditions have celibate bishops as far as i know (I'm not counting Anglicans), but if one wants to think of Apostles as bishops (a questionable move in itself, IMO, though there is some warrant for the view) then this would get dicey, as some were married (Peter we know for sure).
I would be curious to hear this question hashed out.
I think what you say here is very important, although I think you actually argue against your own main point. There are two ways to regard celibacy. It can either mean unmarried, or married but living as celibate. When seen in this wider context I think it is much closer to doctrine than merely discipline. Sure, it is only disciplinary that we only ordain unmarried men, but the fact that men who are ordained should be celibate (married or not) in some regard (at least when speaking of the office of Bishop) this seems to be more than merely disciplinary, for married bishops were expected to live celibate lives. So, pointing to a previous age that ordained married men does NOT mean that celibacy was not expected.
IOW - we have settled into a system by which we have constructed a discipline that highlights a doctrine. But, you are correct to say we shouldn't confuse the two. I think the doctrine is that celibacy certainly has a role to play in the priesthood, and this is best understood when we look at the earliest times of the Church when the "parish priest" as a separate function from the Bishop probably didn't exist. In these times, you only had the Bishop who was expected to live a life of celibacy. As the Church grew, and the extension of the bishop into parish priests came on the scene we went through periods where celibacy may not have been required as strictly for this position, but for the Bishop it still was expected.
I am no expert either, and this all comes from people I have studied. But, I think the problems come from our lack of understanding of the history of the priesthood, and the levels of ordination, etc. It may not be the case that unmarried celibacy is a doctrine of the Church (and is therefore only a discipline) but I do think that general celibacy (for those married or unmarried) has been part of Holy Orders (at least for Bishops) since the beginning and is much more doctrinal in nature than merely disciplinary.
Hope that makes sense.