AFAIK there is no separate version for 64 bit, and I think Developer 6i is unsupported on that architecture. However, it could work.
Are you calling your reports from Forms applications ?
If this is the case, I have read that people have got this to work by replacing som DLLs with the ones from Developer 6i patch 3, since some change in those libraries introduced in patch 4 make them fail under 64 bit OSes.
Those libraries are nn60.dll and nnb60.dll, which reside in the /bin folder.