I've worked for 2 fortune 500 companies that have brought in multiple low payed H1-b visas instead of hiring at the standard US rate. As an engineer I was part of the hiring process. All of the candidates at both places ended up being far less qualified than Wipro claimed and did a terrible job.

So it definitely happens, I'd say it happens a lot.

There are also great H1-b hires like the one I'm working with right now. He is incredibly skilled. He also cant work for another company unless he reapplies so he's stuck.