I know one or two people who use the term "bless them" frequently, as a normal thing to say about anyone (adult, child etc), but generally I think it can be seen as very condescending (perhaps slightly sub-human).
Regarding the heart of your question, my children went to a school with a similar unit, and it has been really good. There are extra facilities which children in the mainstream classes can use, therapists come to visit the school to see the children in the unit, so the rest of the school has an on call relationship, and I think the teachers in general have a better understanding of special needs in general.
My children have not particularly mixed with the children in the unit, but there have never been any issues, and some of the children move in and out of the mainstream, which again is a good thing. The only aggression that they have experienced was from "ordinary" children (although I suspect that neither of the "bad" kids they have had trouble with have particularly stable home lives). I have a feeling that my ds is at least as disruptive at times as some of the children with diagnosed behavioural problems to be honest, and that most schools will have a couple of kids with at least the potential to be disruptive in every class.
The school has an excellent community, and I think that the unit enhances this. Last year for example all the juniors were in a special dance, including those with special needs, and some of them have quite significant disabilities. It was great to see them all giving such a creative performance.