Areas with low percolation rates are one in the same with areas that have seasonally high ground water in most cases

Percolation rate is my reasoning that it may not effect anything at all if he dumps 100g of salt water in the system per month.
The longer it takes to percolate up (veticly) through the soil, the greater distance it will travel through the soil (horizontaly/ path of least resistance).
I see this as a good thing. Greater area for deposits, less concentration.
on the other hand if he lives in an area where the soil percolation rate is very high then he will have to go with the "mound" method you touched on. Due to more reasons than just the salt water

( IE stinky sloshy yard EEEWWwwwww!)
The mound system also requires a sump pump in a seperate dosing tank for the efluent to run off into to be pumped out into a mound set up on a section of your yard with a 15 deg or less rake for run off.
Much more expensive system. ANd you will have an unsightly "mound" litteraly sticking out in the middle of your yard where ever you place it
Your going to have to get it pumped out every year any ways as per regular maintenance procedures of on site sewage any how. SO I would swet it to much.
It IS a good idea to run it by your builder though.
He/She, may be able to modefy your system some how to handle it?
Longer septic field? who knows.
Keep us posted on what they tell ya this is interesting!