My information is that Hammack is evolved from Hammac, a Scottish name, the K added when a group of the Hammac's move into England. The info I have is that the mac is a suffix in this case. Many times the mac is a prefix such MacDougal et.al.
There about three Hammacks listed in ship landings in the early and late 1600's. I haven't got to that point yet. I have traced my clan of Hammacks to James G. Hammack born in Virginia, somewhere, on August 5, 1800.
If you have any shareable information I would be glad to e-mail back and forth.