To put it simply: do own goals count as part of a hat trick?
Usually a Hat-Trick is an informal term, and can be defined by whoever is speaking/writing. So if it was a team-mate you might go for humour and say "Our Striker scored a hat-trick .... but unfortunately one was at the wrong end".
And a journalist might call it "an imperfect hat-trick" , or a special hat-trick, or a hat-trick by majority verdict, or a hat-trick of sorts, or whatever they feel best fits.
But if this term ever needs to be defined in an official way, maybe as part of a sponsor's prize, or for betting, then I'm sure the answer will be no. For example, the betting exchange Betfair defines it like this:
For ‘Tournament Hat-trick’ markets, extra-time is included, however penalty shoot-outs and own goals are not included. In the event of any dispute as to who has scored any goal we will follow the decision made by the relevant governing body.
To make it understandable, the goal credit goes to the player only if he scores for the team. Own Goal credit (discredit) would not go to the player responsible.
Moreover, if state "The player XYZ scored a hat-trick", you would be suggesting that his team has scored 3 goals too. If that player scored 2 goals & an own goal, do the math, his team scored how many goal? Yes, 2. S, that wouldn't make an hat-trick!