Hi Juergen,
can you please clarify one detail: the AMI Hana instance (ami-db546ab2) shows "Other Linux" as platform. First of all, why not SUSE Linux, and second, when purchasing a reserved instance, there is no "Other Linux" option, so can you confirm that selecting "SUSE Linux" there will purchase the matching reserved instance for Hana? I understand that you haven't tried it yourself, however someone at SAP should have the authoritative answer :-).
Cheers,
-- Micha