I've done some reasearch on my own and discovered that DB2 does, as you point out, handle NULLS in the ANSI standard fashion.
I've since spoken with the DBA that set this up and we just have a difference of opinion on how to handle NULLs. I prefer to allow them except where business needs dictate that a value is absolutely necessary and then include the additional login in queries to allow for NULL values (for instance, including the OR x IS NULL condition to WHERE clauses that include nullable columns, as appropriate), where she prefers to use artificial NULL values (i.e. empty strings, 0, 1/1/9999, etc) except where the value will be used in aggregate or mathematical functions. We'll just have to agree to disagree, I guess.