So what Jamie was talking about is the user type thats set on each user as you import them. You can always change this by right clicking on a user and changing the user type. what hes specifically referring to is that if your analyst import is picking up end users it will attempt to update them to the analyst user type as it pulls these peoples information in. So like you found out you can minimize the amount of errors by simply excluding users who are supposed to be end users from your analyst import.
SO important things to understand are the imports all go to the tps_user table and are simply setting a foreign key as the import runs on what type of user the person is.
Another thing to be aware of is that there is an analyst role and an analyst type. Make sure these people who are analysts that you're trying to update are in fact analyst types by right clicking on one of them and choosing "change type". If "analyst" is not an option, then they should be analyst user types and we'll have to dig more into what's going on.