No, all staffs are not merit sources, while the merit source list is not made public, through users merit distribution you can guess who is a source.
Checking the list of most generous merit senders in recent time: https://bitcointalk.org/index.php?action=merit;stats=topsend and also all time: https://bitcointalk.org/index.php?action=merit;stats=topsendat
Would give you an idea of who the 98 merit sources are.