I believe that the view exists so that you can call acs_object_id_seq.nextval.
This needs to be documented better, i.e. somewhere, probably as part of the ad_form documentation. It will bite anyone trying to use ad_form to insert records into a table where the primary key is a sequence but not acs_object_id_seq.
ad_form tries to call yourtable_id.nextval when it inserts a new record and it will it will crash until you dig through the code, discover this trick and define yourtable_id_seq accordingly.