Thanks for posting.
FileMaker Server 7 and FileMaker Pro 9 both use the .fp7 format. Because of this, a database developed in FileMaker Pro 9 can be hosted by FileMaker Server 7 without any issue.
The only limitation would come from FileMaker Pro 7 clients who are accessing the Filemaker Pro 9 database. Any features/functionalities that are in FileMaker 8, 8.5, and 9 and are not in FileMaker Pro 7 will not appear if a FileMaker Pro 7 client accesses the database.
Let me know if there is anything else I can clarify for you!
Sounds like it will satisfy my needs.