Yes, data modules created in FrameMaker will be valid against the relevant DTD or schema. One of the benefits of XML is that the editing application should have no impact on the quality of the S1000D deliverables. You will indeed be able to publish an IETM using FrameMaker created data modules.
All releases of FrameMaker since version 10 have included some S1000D support out-of-the box. Commercial FrameMaker based S1000D editing packages are available too.