That wasn't my experience. I have two lines on iUP. There was a hard pull (for each line) when I originally opened the accounts in 2015, but nothing showed up on my credit score (in terms of pulls) when both lines were upgraded in 2016.
They "pull" credit, but it's a soft pull not hard. Meaning it doesn't show up when others pull your credit (and doesn't affect score) but it can show up for you with some credit montoring services or on your hard copy yearly credit report that you can order for yourself.