I think that's a question for Mr. McDonell.
The names of all of the guests go through the office of the Sergent-at-Arms and corporate security. Some verifications are made, mainly against databases. Just because someone has a disreputable past doesn't mean they will appear on a list of people who can't enter Parliament. The individual in question has been a Canadian citizen since the 1950s, after all. Maybe that's why he didn't appear on any list.
I don't know if I've properly explained the situation.