It seems to me that they are two sides of the same coin - one seeing inherent instability in the propensity of suppliers of credit to overextend themselves and one seeing inherent instability in the propensity of demanders of credit to overextend themselves. Minsky, I think, was on much firmer grounds I think in that he didn't go as far as Rothbard. He recognized that the optimal level of risk associated with leverage is not zero and never called for 100 percent reserves.
But the structure of their concerns are actually quite similar, just on opposite sides of the market (and of course Minsky is thinking more broadly than Rothbard about finance in general rather than just money).
This is just a musing by a guy that hasn't read that much of either of them so I'm curious what you think.