You can generate a menu for AmiWM, running xdgmenumaker like this:
$ xdgmenumaker -f amiwm > ~/.amiwm-xdgmenu
As AmiWM does not support including other files in its settings file, you'll have to copy the contents of the created file in your ~/.amiwmrc. It should be possible to create a script that would generate the main ~/.amiwmrc file from different “source” files, but I'll leave that as an exercise to the user.