This link gives a fairly detailed synopsis of German gun laws in the late Wiemar through pre-war Nazi period:
I can't say that it's a convincing argument on Dr. Carson's behalf. Reductio ad absurdum: If only Poland had been armed, WW II itself might have been averted. Oh, wait, it was armed...
The article makes clear that until 1938 German gun laws didn't specifically ban Jews from owning firearms. Of course, the Nazis probably used the 1928 Weimar era law requiring licenses for new purchases to put extra-legal (i.e. bureaucratic) barriers in place that discouraged anyone the Nazis disliked from exercising their legal rights, but that didn't prevent the continued ownership of firearms already acquired; and discriminatory enforcement of the law isn't the same as legal gun control.
The article also says that the 1938 law (which DID explicitly target Jews) was used as an excuse to cart them off to concentration camps. If this involved round-ups based on preexisting government firearms registration lists, then it suggests that substantial numbers of Jews WERE armed right up to the point where they were imprisoned in concentration camps after Kristalnacht.
The other problem with Dr. Carson's argument is that the Nazis lied to their victims precisely to forestall resistance. Even in the death camps they disguised gas chambers as showers.
When the Jews were initially rounded up in Germany they weren't informed of the conditions awaiting them. The government controlled the media and spreading rumors about concentration camps (most of which had housed political prisoners up to that point, not Jews per se) was defined as seditious propaganda and was itself punishable by detention in such camps.
Once there it was difficult to get out, and many of those who did were immediately deported and thus didn't return to their communities to tell their stories (and if they had, would have been denounced by government informants and sent back -- something they were made aware of by the authorities). Harrowing accounts published in foreign newspapers on the basis of deportees interviews didn't make it past the domestic German government censors.
So, it isn't even clear that armed resistance was a rational response on the basis of what the victims knew before it was too late.
Furthermore, Nazi oppression was organized with all the resources of the state. Jewish resistance at that point was largely individual or at least small scale. The government was constantly accusing Jews of various conspiracies against the state, even when they didn't exist, and employed a block system of surveillance with tens of thousands of informants. Jews were just trying to avoid giving the government an excuse for further repression. Effective resistance must be organized.
The real problem was a form of government which could erase by executive fiat the rights and the very citizenship of a substantial segment of its population. Studying how the liberal constitutional Wiemar republic made this possible is probably a more productive historical research for libertarians. William L. Shirer's book The Rise and Fall of the Third Reich is a gift that keeps on giving.