After reading a little, I am concerned that my 32-bit Delphi application will not be able to use libusb 64-bit driver on Windows 7 and other 64-bit Windows systems, and that it will not be able to talk to my custom hardware device on those systems. Is this true? If yes, is there some workaround? Am I missing something in this picture?
On libusb 1.0 with the WinUSB backend (Microsoft driver included with windows) we have no problem to communicate with it from an x86 app (Managed c++ library used by C# applications). The behavior is the same on both x86 and x64 platforms.
I don't know about libusb 0.1 (The old one that is able to use the libusb-win32 kernel driver) but as your link point to the 1.0 version you don't seem to use that.
At some point libusb 1.0 will support the libusb-win32 kernel driver but except in specific cases it isn't necessary (WinUSB have some limitations but I never ran into them)