I agree with your reading. Those are all very likely to be the same persons that I was proposing as "possible" therefore I might be quite biased. Just because I've not seen Haka as a variation of Haagen before doesn't mean it surprises me much.
Remember the great Y2K software panic? That was actually the year I was really getting into my own family research and was struggling with what I considered the great G2K panic in Norwegian spelling. Sorry -- pointless personal story.
If it was my family I'd want to check the birth/baptisms and perhaps also the confirmation records for the other children listed in the book as born to Haagen and Ingebor. A study of spellings from those records and matches to the published book info would probably make the "preponderance of evidence".
Page 57 of the bygdebok seems to discuss the history of the farm's name(s).