In short, yes. As you can see on the following page from
MySheetMusic.com, all of the Hanon finger exercises are
available to be printed for free, using the Scorch ActiveX
playback and printing interface, which you might need to
install if you want to test it out:
Even guests to the site who are not registered members
can print the sheet music for free. They could not do this
if these scores were not in the public domain.
As noted on this page from PDinfo.com:
"Specifically the last paragraph of Page 3 states in part
'Works published before January 1, 1923, have fallen into
the public domain.'"
Information about public domain and copyright protection is in
'Extension of Copyright Terms', Circular 15t, of the U.S.
Copyright Office, in this PDF file:
The Hanon exercise scores were first published in 1900, and
so are in the public domain.
DanmansMusic.com clarifies this on this page:
"The Hanon Exercise program (which was first published in 1900,
and has been used by classical musicians/teachers ever since)
is, in my opinion, the best out there - and you can download
it for free in our Free Sheet Music section."
Additional information may be found from an exploration of
the links resulting from the Google searches outlined below.
Searches done, via Google:
hanon finger exercises
"hanon finger exercises"
"public domain" "published before OR prior"
hanon finger exercises "first published"