Is this wiki related in any way to the GTA Wiki on wikia ?
Yes - we used to be.
User:Gboyers founded Grand Theft Wiki in 2006. In 2010, the community became very unhappy with Wikia (the company) and the way they were taking over the wiki, making unpopular changes, and changing the site away from its original values.
So in October 2010, Grand Theft Wiki moved away from Wikia to grandtheftwiki.com, after a big community discussion, with almost all users in favour. This site is now owned and operated entirely by its users and staff with the goal of making an awesome wiki - not about making profit.
Unfortunately, Wikia did not want to lose the money they made from advertising on our site, so they decided to keep running a dead copy of Grand Theft Wiki. They banned all the staff, promoted staff admins didn't know the wiki at all, and removed all references to the new website, and they kept the URL we used (gta.wikia.com), so even now a huge number of users go to that site without knowing we moved.
Now, Grand Theft Wiki is a high-quality wiki with awesome staff and users; whilst the GTA Wikia is a mess. They do get more traffic, but the way that site is run is awful. For example - draconian policies that banned new users who don't know how to edit perfectly, staff that don't have the experience our staff do, and a big focus on money with the site covered in advertisements.
We may not be as busy as we would have been if we'd stayed at Wikia, but this site is a million times better.