Do you use MCCC? Occults in TS4 are just hidden traits, so if you use MCCC you can use it to export a log of a Sim's traits which would show even the hidden ones and that will tell you which occult type they are.
Another thing I've done, in my game, is create a club for each type of occult that only accepts members of that occult type. With those clubs set up, I can see if a Sim is an occult type just by checking if they are eligible to join the club. Babies can't join clubs though, so you wouldn't be able to check with this method until they are toddlers.