Gamestudio doesnt have hint blocks or portal brushes or anything like that, what you can do to block rendering is setting a blocks faces all to none texture flag
the only problem with that is the block gets rendered solid black, so there pretty much usless for blocking items behind them. It would be great if map entitys would block rendering, but they dont!, so if you have door map entitys with a very detailed room behind them, when you look at the doors everything in the room behind them gets rendered as well.
Best thing to do is use curved hallways and things like that, because you can slow it down to a crawl if you have lots of long straight shaded areas, even worse if your adding terrain into the mix