I have noticed when looking at many wheels on Summit's website that many ones are rated for 30" tall tire only (not including slicks). But I still see many pro-street cars with weld prostars and such with tires taller (like 33x21.5) when technically it is not considered safe?

The only ones I have found other than Weld Aluma Stars (which are more of a drag racing wheel) are the Weld Weldstar RT's.

What is the deal with this?

The issue comes from the fact that a tall tire will tend to have a lot of sidewall roll to it in a panic situation. I run the Weld Superlites on my car with 32" slicks.

According to Summit, slicks are fine. It is just the street tires at that height that are not approved.

According to Summit, slicks are fine. It is just the street tires at that height that are not approved.

Right, because the slicks will never see a panic swerve on the street. They do not see the side loading of making turns at speed either.