Can a conference paper with all weak reject get accepted at the end? Those who have experience in setting in conference program committees: can a paper with all "weak reject" reviews get accepted for publication at the end?
If nobody wants to accept the paper, it shouldn't get accepted.  This holds even for workshops and symposia with very loose standards, as the reviewers should be making their judgements based on those standards (e.g., "this paper is pretty half-baked and poorly written, but we're just looking for interesting ideas to discuss, so it's a weak accept").

Thus, the answer ought to be no, it cannot be accepted (except in certain unusual cases, such as the organizers deciding there is a hidden nugget with value enough for shepherding to improve the paper).

A struggling, eccentric, or fraudulent organization, however might just not care, and accept it anyway. If you have this happen to a paper of yours, you may wish to reconsider whether you really want to publish it in that venue.