The solution turned out to be relatively simple (yet I never found it anywhere online for some reason…)
I set up some functoids in the map that used the logical date
functoid, and if it was a logical date, then a Value Mapping functoid
sent the value to the datetime field. The logical date functoid also
went to a logical NOT functoid which then went
to two Value Mapping functoids. the first value mapping functoid
returns the date of 1901-01-01 to the datetime field, and the second one
simply returns the constant true and goes to the IsNull attribute in
the datetime field in the destination schema.
Summed up, I never found anywhere that said the datetime field needed
to have a valid date in it in order to set IsNull = “true” for it to
work…