i) The dumped files are already available from Lisp, as the elements of
`preloaded-file-list'.

ii) Function and keymap autoloads in dumped files are silently ignored,
cf. the #'autoload docstring:

"...

If FUNCTION already has a non-void function definition that is not an
autoload object, this function does nothing and returns nil."

This is not true for non-function autoloads, though. Here are the dumped
files that currently have autoloads that are picked up while
constructing auto-autoloads.el:

("mule/mule-composite" "x-win-xfree86" "x-win-sun" "newcomment"
"menubar" "cus-file")

Those autoloads should probably be removed, in general. But that's a
separate issue from whether autoloads in dumped files should be ignored,
and I personally don't think the latter is worth it.

It should be possible to set the finder keyword "dumped" on files when
the dumping process is done.

The only counterargument I can think of is that if the keyword isn't in
the file, users may put ;;;###autoloads in it.

Maybe autoloads in dumped files can be silently ignored?