Actually, yes you can...
Ordinarily (>99% of the time) Folder Actions are used to process the files dropped in a folder. That completely ignores the other oft-overlooked parts of Folder Actions.
Folder Actions can also trigger when files are removed from a folder, or even when the folder's window is opened or closed in the Finder.
Ultimately, though, all of these are just triggers that initiate the script.
There is nothing that says the Folder Action is restricted to the new files.
Ultimately you could write a Folder Action that just looks in the folder for ANY .jpeg file and moves it to the destination. This will catch any .jpegs that weren't moved in a prior invocation due to the race condition that you describe. In this way you completely ignore the dropped files because they're irrelevant to what you're trying to achieve
on adding folder items to this_folder after receiving listOfAlias
tell application "Finder"
set files2Move to every file of folder this_folder whose name extension is "jpeg"
move files2Move to folder "JPEG Images" of folder (path to desktop)
end tell
end adding folder items to
Now if any JPEGs are skipped in error, they'll just be moved over the next time any file is added to the folder.
Or you could change the action to a 'on opening folder' action so any residual files are moved when the folder is opened. All kinds of possibilities.
