Your problem is the control characters. Try the following:

my $cmd = "/usr/bin/man ssh";
open(MAN, "$cmd |") or die "Cannot run command '$cmd': $!";
while (<MAN>) {
  s/\010.//g;
  print "Worked!\n" if /ssh/;
}
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The \010 is the octal escape sequence for character 8. You can double-check the presence of character 8 by:

man ssh |perl -ne 'print "$&:", ord($&), "\n" while /./g' | less
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