Hi Angliholic,
After reading some sentences in contexts that include the phrase "make money off of (sth)"/ "make money off (sth)", I have a feeling that the two last sentences somehow have the same meaning as the two first. However, they bear a little difference related to time to do the job for money - I mean the money makers (when using "make money off of (sth)"/ "make money off (sth)") just have an intention of making money in that way (by selling seal skins) for the short period of time when they seize a golden oppotunity. Meanwhile, using "make money from" seems to indicate that selling seal skins is the main and permanent job.
Hope that my explanation here is clear enough! Moreover, I find these sentence very interesting, thanks!