It depends if the immigrant is hired because the native worker is deemed too expensive. In this case, it contributes to reducing contributions through wage suppression.
Given that the company sponsors them and come from lower incomes countries, they are ready to accept lower wages. If they do it I don't see why everyone wouldn't be doing the same.
It's of course hard to prove formally as those companies will comply with regs to make it look like they aren't discriminating (fake job ads, etc...). By the way in the US Indian consultancies got busted for this.