Interesting questions, I did some research in my Chiltons Manual. My 1994 Ford 460 V8 has multi-point (or port) fuel injection and requires a system pressure of 30-45psi. Earlier multi-point systems from 1988 through 1990 used two pumps, a low pressure in-tank pump and a high pressure externally mounted pump. This earlier EFI required 33psi system pressure.
As far as an external pump being able to draw fuel through a failed in-tank pump, it appears that the typical in-tank fuel pump is either a centrifical pump or gear pump (like your engines oil pump). System check valves are to keep system pressure from leaking off when the engine’s shut down. In other words it looks feasible to be able to draw fuel through a failed in-tank pump. Here’s a YouTube discussion of fuel pumps http://www.youtube.com/watch?v=QbzEeWy1b3o
