This probably doesn't matter, Qassim's father was an Arab Sunni while his mother was a Kurd Shi'ite.
What do you mean "doesn't matter" ? Like I said many people at the time didn't know whether he was Sunni or Shia. And BTW, the Wiki article quotes one source on this. This is still under debate.
Now even if he was a Sunni, it didn't affect his governance in any way.
Here is a photo of him visiting Shiite Ayatollah
Muhsin Al-Hakim:

WOW! What a man IA, wish we had more people like him in this world [ in each and every country]. He is an epitome of a true nationalist. Iraq should give him the highest honor possible.
He's still immensely popular among the communists, leftists, feminists, religious minorities and the disadvantaged. There is talk of building a statue of him in Baghdad. Sunnis generally don't like him because he opposed Nasser, pan-Arabists, and socially conservative tribal sheiks.
I don't wanna portray the man as an infallible god. I do have issues with some of his policies but I shouldn't go into details now. I don't want to hijack the thread anymore. Maybe another time.