NS credentials won't work in Nitrobetting since they are separate services, and that means stand alone databases. Both sites share their Sportsbbok Poker and a casino provider (Concept Gaming, although, Nitrobetting is running Nucleus' games). The main difference is that Nitrobetting offers Sign Up and Reload bonuses up to 50 mbtc.
Of course, you can't have the same credentials working for both sites. It's like trying to log into Bittrex and Bittrex global or Binance and Binance US using the same credentials. It doesn't make sense, does it?
They are two sites offering different products but still sister sites. However, if the reputation of Nitrogen sports is already tinted. I would be so careful with Nitrobetting as well. They are the same people.