I kinda expected a poll like this
No ZZ Top are not hard rock. They are a southern rock, blues rock, rock band. But that doesn't mean they can't boogie in a hard way
Hard rock is Black Sabbath, Motorhead and Judas Priest. I wouldn't even consider Led Zeppelin or Deep Purple hard rock, let alone ZZ Top.
Black Sabbath, Judas Priest, Iron Maiden Ozzy and Motorhead are heavy metal.
Led Zeppelin, Deep Purple, AC/DC, Aerosmith and Uriah Heep are hard rock.
ZZ Top is blues rock