No, you should not post such answers. That's not an answer to the question; saying that you can't replicate their problem is just a comment.
You shouldn't be posting an answer at all if you feel that it needs to be updated based on later input from the OP to be a true answer. You should feel, at the time you first post it, that it's an answer to the question. If not, you shouldn't post it, you should post a comment until your clarifying questions are answered.
The question should also be closed with the offtopic sub-reason reason of:
Questions concerning problems with code you've written must describe the specific problem and include valid code to reproduce it. See SSCCE.org for guidance.
Since the problem can't be replicated with the information given.