Was "Rascalism" ever used to mean drapetomania?

There is a connection between the words, different to that you suggest, which can be found in Cartwright's writings though they are pretty stomach-turning, even for their time.

Cartwright's vile nonsense invented not just drapetomania, also dysaesthesia aethiopica which was likewise supposedly a disease only found among people of African descent, but which made them "lazy" and prone to "mischief".

Since he also claimed that physical lesions were found on those afflicted, it would seem that he had found a way by which both those who were suffering from any one of the great many illnesses that can deplete ones energy, along with just about any behaviour or lack of behaviour that overseers disapproved of, and lump the whole thing under dysaesthesia aethiopica.

Suffering from influenza symptoms? Must be dysaesthesia aethiopica. Not meeting some arbitrary quota of work? Must be dysaesthesia aethiopica. Objecting to anything a white person says? Must be dysaesthesia aethiopica.

In all, there wasn't really anything he wouldn't claim was caused by either dysaesthesia aethiopica or drapetomania, if it suited him. It also allowed claims that wounds from beatings where in fact the "lesions" from the dysaesthesia.

Since he claimed that free men suffered from it more than slaves, he could therefore claim slavery as something which was good for the slaves.

It was Cartwright himself who said that this, not "drapetomania", that was also called "rascalism".

In doing so, he was deliberately tying his self-serving racist ramblings to an existing word with negative connotations, so he attempted re-purpose rascalism and rascal, rather than either of them originating from his "theories".