I remarked recently that Coach Joe Paterno was the most powerful
PROFESSOR among Penn State's faculty, and a critic stated that he is
not a professor. Is Joe Paterno considered by the University to be a
Professor of Football, or any other kind of Professor? Does he have
the rank of a professor ?

Hello.

Yes,  Joe Paterno is a professor on the Penn State faculty. 
Specifically, Paterno is a "Professor of Physical Education."

From Penn State's official faculty roster:

"JOSEPH V. PATERNO, B.A., Professor of Physical Education"
source: Pennsylvania State Univerity - Faculty: Kinesiology
http://www.psu.edu/bulletins/bluebook/faculty/kines.htm


From another Penn State web page:
  "Joseph V. Paterno, Professor of Physical Education says, (p. 4),
The knowledge and skills that you learn studying the humanities, arts,
and sciences give you power to understand, the power to set the course
for your own life, power to exercise your freedoms and to affect the
community around you.  With all of your education so widely ranged
these powers are easily acquired. "
http://www.personal.psu.edu/users/d/c/dcm247/pg2Mind.html

Paterno's status as a professor is also mentioned in the newsletter of
the Pennsylvania Classical Association.

"These financial grants... are endowed by the generosity of Professor
Joseph Paterno and his family to assist outstanding students enrolled
in Greek and Latin courses at the University Park campus of Penn
State."
http://www.dickinson.edu/prorg/pca/newsletter_w03.pdf

-------
search strategy:
"joseph * paterno" professor site:psu.edu
"professor joseph * paterno"
"professor joseph paterno"

I hope this helps.

Thank you for the tip.
-juggler