The novelization was NOT ghost-written. We have confirmed with GR's assistant, Susan Sackett, that Alan Dean Foster was not involved, only writing the "story" of "In Thy Image" (which Harold Livingston expanded into TMP), which he drew out from Gene Roddenberry's unfilled "Genesis II" script, "Robot's Return". ADF has also confirmed that, until the 2009 novelization of the first Kelvinverse movie, the "story" of TMP was his last Trek work after numerous assignments in the 70s.
At the TMP Appreciation FB Group, we suspected Susan herself of co-writing it with GR, or ghosting for him. She has confirmed it was not her, although GR, as a first-time novelist, did have some minimal help from a published novelist as the deadline approached, who will continue to be unidentified. But this is not rare. Most professional authors have at least one Beta reader who helps to shape the look of the final draft. It was not a ghostwriter.