I want to do world records for THUG PRO. For instance most spins in an air. or longest grind. is it possible here? Or would I need to go to a different site? I know its not technically a speedrun...

If it's not possible to turn it into a speedrun then it'll instantly get rejected but unless you try and make it into a speedrun no one is going to know rather it gets accepted or rejected since we also know nothing about it.

Just from the sounds of it, I'll save you a little bit of time and suggest that you ask the moderators of Tony Hawk's Underground 2 for their opinion and input since from the wiki source its a type of mod of the game. https://www.speedrun.com/thug2

Note: In the meantime, even if you wanted to submit this to the site for review we have rules in place that users need to connect some form of social media to their account (this is to make life easier for other people that need to get in touch with you regarding the game/mod in questions at any time) and you need to be registered on site for a minimum of seven days.