It's probably not necessary for the head honcho to be on the HACCP team, as long as regular management reviews are caried out with senior management present to review strategic system performance, resourse requirements etc.
It's an interesting question when you come to the "senior management commitment" section of the BRC. Perhaps there should be a once or twice a year review with senior management or if there was a major change / major rewrite.
The fact is though I'd rather have people in the team who know what really goes on (i.e. the operators, shop floor team leaders etc.) but it could be good to use it as a tool to get funding for those long standing food safety issues you never seem to get signed off...