PackageMaker alternative?
There's two alternatives I'm aware of for PackageMaker that would work in this situation:


A third-party tool named Packages 
Apple's pkgbuild and productbuild tools working together.


If you're planning to add packages to a NetInstall set, you should be aware that Apple made an undocumented change in Yosemite. If you add any additional packages for installation as part of a Yosemite OS install/upgrade (like you would with NetInstall), they must all be distribution-style flat packages. 

Bundle-style packages (like those created by PackageMaker) will not work when added to a Yosemite OS install/upgrade and component-style flat packages also will not work.

For more information, see Further note on additional packages and Yosemite.