Nickolay is correct, the osxfuse distribution package cannot be included in another distribution package. This is a limitation of the package format. Distribution packages may only include component packages but no other distribution packages.
Do not do this!
The official osxfuse 2.x distribution packages contains three slightly different versions of osxfuse. One for Mac OS X 10.5, one for Mac OS X 10.6 to 10.8 and a third for OS X 10.9 and 10.10. The osxfuse distribution package will install the correct version depending on the version of OS X you are running.
As you know osxfuse consists of three parts: core, preference pane, and MacFUSE compatibility layer. When updating osxfuse the official distribution package makes sure that all components stay in sync.
osxfuse is a shared system component. Messing with its installer can have adverse side effects. I cannot stress enough that it is a really bad idea to extract individual component packages from the official osxfuse distribution and re-package them.
The proper way to include osxfuse into your distribution package would be to add a postinstall script and install osxfuse by invoking:
sudo installer -package /path/to/osxfuse.pkg -target /
As a side note, a number of people have complained on this mailing list about osxfuse "magically" appearing on their Macs without them installing it. In my opinion it would be preferable to inform the user that your app requires osxfuse instead of installing it silently.
Regards,
Benjamin