Earlier quoted context omitted.
No, substring searches. Ctrl+R in bash (by default, at least) will not search from the middle of a command. For instance, if the previous command was "hello", searching for "ello" will not bring it up. Whereas with zsh, it will.
The default bash on OS X (3.2.48(1)-release) just did when I tried it.
> ell
Completing external command
git-shell xdmshell xkbbell
Completing shell function
_ispell