Yes, definitely damnable.
I'm not convinced that an explicit belief in salvation by faith alone is always necessary to be saved (key word being explicit.) However, it is necessary that one trusts solely in the finished work of Christ alone. If anyone who adds baptism as an act which they perform which contributes to their salvation, then Christ has become as nothing to them.
I don't believe damnable heresy can be forgiven without being repented of. One might sometimes have doubts, or confusion, about the true gospel, and still believe and be forgiven, but any who believe and trust in a false gospel are unforgiven and unsaved.
I know a woman on another discussion board who belongs to the Church of Christ. I asked her once if her church believed that baptism was needed for salvation. She pointed me to a website where 2 CoC pastors were arguing the point, one saying it was necessary, another that it was not. They were having a semi-formal discussion on the issue; I was amazed, two pastors in the same denomination openly disagreeing as to what the Gospel was, the same way two Presbyterians might disagree about pouring or sprinkling to baptise babies. This was about 5 years ago, and I don't have a link to the website any more.
I understand that there is a severe problem in believing that a certain act, i.e., physical baptism by immersion, is necessary for salvation, and I can never hold to such a stance, but I'm not sure if it's as heretical as it seems. At least, it's not trying to say, "Be a good person and go to heaven" -- it's not as bad as Catholicism. Yes, I realize that by making a specific act required for salvation, the Church of Christ advocates a mild works-based salvation, but as I said earlier, I see this as very similar to Arminianism.
The analogy that Al Maxey (the "this guy" in my previous post) used for the doctrine is the following:
Suppose I place a million dollars in a bank in your name and then inform you of this fact and tell you it is a gift from me to you, and that you don't need to work for me to earn it. It's free! I then inform you as to the conditions for accessing this GIFT. You must go down to the bank next Wednesday at 4 p.m. and see the Vice-President who will have a simple release form for you to sign which transfers the money over to you. Will you comply with these conditions, David? If you don't will you be able to draw from those funds?
Of course, he follows this by claiming that accepting this gift is not worth any merit, with which I respectfully disagree, but it is clear from this analogy that the sensible Churches of Christ are only Arminians.
Of course, if you believe that all Arminians are damned, then it's a different story.