Resort fees are generally per room, or reservation, not per guest. For example, DVC charges a $190 resort fee if you have one person in the room or eight.
Some resorts may do this differently, as there is no standardized way resort fees are implemented.
The resort I own, the Grandview, charges a $30 fee. However, that fee is waived if you are an owner of the resort. Despite this, I see complaints on Facebook from owners who say they were charged the resort fee, so these rules may not be always perfectly implemented by staff.
Also, someone who books a 4-night stay at the Grandview pays $30. Someone who books a week also pays $30. Thus the amount of money you get from these fees is going to have some variance. Again, The Grandview would not know if I have one guest in the room or 8.
Also, is it possible that some resorts remove the fee for a bad experience or to calm an angry guest? I could see that happening.
In any event, while a resort should have pretty solid data on how much it will collect over the year in resort fees, it's not going to be like collecting maintenance fees and will likely have some variance.