The (statutory) board should explicitly accept or reject council recommendations made to it, if any, and the board's minutes should be certain to document its acceptance, rejection, or decision to take no action;
It is unlikely that all the council's suggestions will be brought before the (statutory) board, but even suggestions that are not submitted should be covered by file memoranda. These records document the council's independent thinking and affirm its separation from the board. 3
My experience with advisory boards has been much more informal in the structure, process, and linkage with the advisee organization with a minimum of paper trail involved. The legal points suggested have been carefully set forth in the advisor's contract with each individual advisor. His or her obligations and liabilities in the relationship are carefully spelled out to ensure distinction between the advisory role and any statutory board role.