Let's see, I've been using brass hardware on the exhaust system for the last thirty years or so, and putting RTV Copper on exhaust gaskets as a matter of course for at least twenty - and having no trouble either way. So, you'll be fine.
Theoretically, NPT doesn't require the use of sealant - but I know I feel better if I use the stuff anyhow. RTV Copper - I've not quite worked myself up to using PTFE on anything that runs over 500*F, no matter what the label sez...
"recon" (sic - reckon)(tm) "hihgly"(tm) "seceed"(tm)
"Outback AIDS - Alcohol-Induced Dizzy Spells"