In doing a Tutorial for creating FTP accounts, this is some of what I found to apply for that area:
Characters Allowed
Although you can use almost anything for creating an ID and/or PW -- and get a message saying &successful& -- some special characters cannot be used. All special characters keys on a keyboard, can be used for inclusion within an ID and/or PW except for the following:
& ampersand
( left parenthesis
) right parenthesis
| separator (found on the same key as the backslash)
; semi-colon
& left angle bracket
& right angle bracket
Note: as odd as it may sound, you can even use * (shift+8 key) which amazes me!
The bad news is, Cpanel will &always& show a successful setup, even if it will not work for an FTP account. It was only through trial & error (using every available key on a keyboard) that I was able to determine what worked and what didn't.
Although the &not allowed& characters listed above will not work anywhere within an ID / PW, I was able to setup a FTP account using a Numeric character for the first digit.
So it may be a handy (relevent?) reference for Hosting Account setup, but should be taken with a grain of salt.