My ultimate take:
In a single shot or vintage Black Powder Bolt Action like a Mauser 71/84 there is no real issue other than convenience not to just use black powder and totally avoid any possible problems.
The rub comes with double rifles and the relatively common problem of barrels shooting too far apart because of some "weaker" or "dirtier" modern black powders. In this case it sometimes becomes necessary to use Nitro for Black loads or maybe duplex loading.
That's my 2¢ worth…..
- Mike