I looked around the source code and it seems that DATA_TYPE is hard-coded into the source with no obvious options for using an older DB schema.
If this is the case, it looks like my only two options are to forget about using DF until I can get the DB upgraded (perhaps never) or resort to some local hackery of DF to make it ignore the DATA_TYPE field. It's too bad because for store procedures, that field is supposed to always be NULL anyway.