WHERE baas_id != 0 may not work. Usually it's written as l WHERE baas_id <> 0;
Also, if you load exactly the same fields then the data ends up in the first table. If you don't want that you can specify the noconcatenate keyword:
noconcatenate load ...etc
But you'll get a massive syntethic key.
You can rename the fields or use the qualify keyword:
That's also not a good idea. The best plan is to load the Persons table as it is with both the bedrijfsleiders and uitvoerders. You can use the baas_id field in expressions to distinguish between them.
There's also the possibility to create a hierarchy table using the hierarchy keyword. Look at this discussion for an example.