I have three teirs of responses to references.
1) Level One. I will just let them know I worked with them, in what position they filled, and the size of the show; and let them know if they were hired again. (by not saying anything but the simple facts, most people will read that as a non-recommendation, and thus avoid any tricky legal background.
2) Level Two: I will ask about the position they are applying for, and then compare that with the work they did on my show.
3) Level Three: I will give a glowing recommendation.
I am one person who actually sued a formal employer about something in my personnel record. I left the job for family leave, taking off three months. One month into, I decided not to return; thus giving two months notice. Although my entire tenure in the position I was reviewed at 90% or above, and had glowing inter-departmental notices, I was marked down as "do not rehire". I didn’t know this, as was getting turned down for other jobs based on that one box checked on my resume. (There was not one valid reason in any job evaluation to mark as such.) A couple of letters from a lawyer, I was clear, my legal fees paid, and a small settlement. Just be careful what you are saying.
In the end, you do have to be careful with references; both from giving a negative as well as giving a false positive. (I hate these – according to every resume and letter of reference I get for internships, most young SMs out there should be stage managing on Broadway.)
I just wish people would be a little more realistic in references so they carried more weight and meaning, rather then just be a glowing reference.
This is why I am much more likely to contact a non-listed reference off you resume if I know them personally.
My 2 cents.