There are many ways to create footprints nowadays.Some companies ( Linear, Microchip, Texas ect.) use UltraLibrarian and they distribute their footprints being as bxl file and you can convert this file into any format such as Allegro,Mentor Graphics, Eagle etc. It's really nice method.It creates schematic view and footprint simultaneously.PartsQuest also supplies foorprints and schematic views onlinefor mainframe PCB CAD tools.
Yes, this should be the way to go. There are other ways, too.
But in this case, the footprint information is not in the datasheet (but Intersil give footprint informations in other datasheets), and additionally there is no reference to a standard package (like JEDEC..).
I´d say this is a task for the Intersil support.
Or make your own component footprints based on the component dimensions from the data sheet using the PCB library expert (a version available for free) at pcblibraries dot com.
If you use the manufacturers footprints for everything you may find that you end up with a dozen different extremely similar footprints which could all be covered by the same footprint.
IPC-7351 especially if you have limited experience, most PCB designers have limited experience these days, many don't ever get hands on experience actually assembling the boards they design.