Nope, Nitrogen works perfectly in PCPs.... Just make sure you don't have a "mixed gas" in your welding tank.... Bobno worries there ,got it from my brother he works at a welding supply store, I'm just worried about getting the press-flow rate right, proberly just do it till the nitrogen pressure falls below 500 psi . But if it increases efficiency might be tempted to try again
I do almost the same thing. Fill off 6k nitrogen until it's too low then I use my Yong Heng in "booster mode" and feed it 5 psia nitrogen from the nitrogen tank. Speeds up the fill time by about 50% and also means there is no moisture at all going in. But I wouldn't feed it more than 5-10 psia the YH first stage compression is fixed at 10:1.