1) No there is no way to limit iOS options to just take picture.
2) There is not an option in the windows version for taking pictures in filemaker. Windows runs the full version of filemaker. Filemaker Go is for iOS. There is not a Filemaker version for windows 8 RT. You may be able to gete a plugin to intergrate with the full version of filemaker.
Feature Request can be made at : http://www.filemaker.com/company/contact/feature_request.html
There is a Filemaker Go Forum... iPad / iPhone / iPod runs Filemaker Go.
I don't mean to suggest that filemaker will not run on Windows 8 RT, because I don't know. It is not listed under system requirements. It just states standard and professional.