They didn't even check uploads in the Sims1 days. TSR doesn't care where the content comes from.
A quote from
2002! from Dov Sherman from Otakuworld, one of the early artists who managed to make custom meshes:
I tend to stay away from TheSimsResource because they have so much stolen artwork. It's not that they deliberately host pirated art; they just don't make any effort to avoid doing so. I've had to contact them on numerous separate occasions to have the same skins (posted under different other people's names) removed. I had been planning to send them my Usagi and Ryoko Sims but I changed my mind after the eighth time I had needed to get them to stop distributing those very Sims under someone else's name.
From what I have heard, they're currently being sued by people whose paintings were turned into Sims objects and then sold on the TSR CDs.
If someone steals your stuff once, that can happen. Twice? Raises concerns. But 8 times? Obviously even back then nobody was checking stuff, and I doubt that has changed over the years.
When I looked through their Sims1 stuff one day (for laughs) I still saw lots and lots of identical stuff listed under different creators, and I imagine there's lots of stuff lifted from other creators in the Sims2 section too.
Actually, now that Securom is gone I hope Sims3 doesn't tank. Just think of all the cool kids who will deinstall Sims2 to switch to the newest shiny toy - all lost money to TSR and other paysites, especially if the new Eula stays the way it is and everyone and their dog may modify and share stuff.