Currently, Aha! only pulls custom fields for mapping to Rally. However, there are other fields built into Rally (Such as Investment Category) which could be mapped to custom fields in Aha!
We should investigate and see if there is a way to pull all fields from the rally type definition without pulling an overwhelming amount of data.
The status of this idea was out of date. Since this idea was created we have added the ability to map fields in Aha! to both custom and standard fields in Rally.