Not really, if the fear is being sued for wrongful dismissal. If the advice is so non specific that it doesn't contain anything actionable, then it's probably not specific enough to be helpful.
Essentially, if you give the ex-employee anything concrete to work on ("You could improve on skill X"), then the fear is that they'll demand clear evidence that they were deficient in that area at your workplace, which you probably don't have. Now you've weakened your case should the employee bring a wrongful dismissal lawsuit (under whatever laws apply in your state/country). Hence the reluctance to say anything at all.
It's not right (morally), but it's understandable.
This is why I'm skeptical of the value of things like ENDA. Without some higher level data collection to see trends in hiring and firing at a company, it would be hard to prove someone was fired for something other than performance since no one will even hint at a reason. Those demographic checkboxes on applications don't help if the people most likely to be targeted don't trust an employer to use it properly.
Reminds me of a friend who used to manage a fast food outlet, it was corporate policy to never fire anyone, they simply would schedule the person 0 hours week after week until they quit.
Essentially, if you give the ex-employee anything concrete to work on ("You could improve on skill X"), then the fear is that they'll demand clear evidence that they were deficient in that area at your workplace, which you probably don't have. Now you've weakened your case should the employee bring a wrongful dismissal lawsuit (under whatever laws apply in your state/country). Hence the reluctance to say anything at all.
It's not right (morally), but it's understandable.