This question popped up first, of course, when I googled up "URL safe characters", as most people would. I think it's worthy to put up a straightforward answer to a concise question. From the horse's— ugh, RFC2396— I mean, Sir Timothy's mouth:
2.3. Unreserved Characters
Data characters that are allowed in a URI but do not have a reserved
purpose are ...
Whether or not you use the "subpage" feature in WordPress should have little impact on SEO. When you use that feature WordPress does two things:
The URL of the subpage starts with the URL of the parent page.
The subpage contains a link to the parent page.
URLs don't really matter for Google SEO right now. Google doesn't put much (if any) weight on ...
I don't see this is affect to your SEO. It just treated it as a new page of yours. However, I think your user will be confused as your link was quite same to another.
As long as you said, content, meta, title etc are the same, it is ok for SEO.
Hope it helps!
Not totally sure of why you're trying to do this? Maybe you can add more information.
If you want to pull content from another server or location, there are several ways to do it - virtual directories, RSS feeds, etc (see links below). However, if you are trying to hide the source of the content from the user, Google would probably interpret that as ...