I added some additional notes and sources to the disputed origins section of this profile and disconnected the parents since this thread has gone a year without a single comment. All the sources I have read agree with your conclusion that he could not be the son of Thomas Hammon and Rose Tripp but I added internal links to them for purposes of curiosity. Anderson specifically states in the 2015 Great Migration directory that it has not yet been proven that he is son of William and Mary of Melford as proposed by Frederick Hammond. However, he doesn't say it is disproved either. Feel free to edit my notes.
As far as the spouse she should probably be Elizabeth Unknown. If we don't know his origins there is no way we can determine who he married without further evidence but I left her be for now.
Disputed Origin
According to The Great Migration Directory: Immigrants to New England, 1620–1640 the parents and origins of this person are not known.[1] Frederick Stam Hammond, History and Genealogy of the Hammond Families in America, volume 2 (Oneida, New York,1904) 1-5 proposed that he was the son of William and Mary (___) Hammond of Melford who was baptized in Melford Parish in Sept., 1603 with his brother John. Anderson says specifically that this has not been proven to be the immigrant.
Previously NEHGR, p. 28: Vol. 30 in 1876 stated erroneously that Thomas Hammond of Hingham was the son of Thomas and Rose Trippe, They did have a son Thomas born 1586, but the same parish register notes a Thomas died the same month, The will of the father, in 1589, lists no son named Thomas, but lists all the other children. Hammond clearly not noticing the death of their child and the lack of mention of his in the wills of his parents. So we can be fairly certain that he was evidently not the son of Thomas Hammon and Rose Tripp of Lavenham. A recent discussion of the will of Rose (Trip) Hammond - Stewart is given in NEHGR 150:433 by Anderson.
A Thomas Hammond married Elizabeth Cason of Lavenham, in 1623. No reference to parents of either. As this is a very common name it is uncertain which Thomas this was. NEHGS, Vol. 107 p. 226 in in 1953 stated that Thomas Hammond of Hingham, married Elizabeth Cason, daughter of Robert and Prudence (Hammond) Cason but this lineage appears to be submitted by a family member.
The Great Migration Project as of 2015 concludes that the evidence is no sufficient to determine his parents and origins. Although we can not disprove that he was the son of William and Mary (___) Hammond of Melford.
[Note 1: Thomas and Rose (Tripp), although they are confirmed as the parents of William Hammond of Watertown. The Great Migration Begins: Immigrants to New England 1620-1633, Volumes I-III. (Online database: AmericanAncestors.org, New England Historic Genealogical Society, 2010), (Originally Published as: New England Historic Genealogical Society. Robert Charles Anderson, The Great Migration Begins: Immigrants to New England 1620-1633, Volumes I-III, 3 vols., 1995). See also: NEHGS, p. 28: Vol. 30: 1876 in which Thomas of Hingham is attributed to Thomas and Rose. ]
[Note 2: Thomas Hammond of Lavenham, husband of Rose, died in 1589, his will mentions: wife Ruth, son William, daughters Rose, Martha, Marie, Susan, and his sister Margaret Jollye: No mention of son Thomas. Same text notes: Thomas baptised Jan. 9, 1585 died on Jan. 16, 1585. See: source notes below: (p. 51-52) History and Genealogies of the Hammond Families in America : with an Account of the Early History of the Family in Normandy and Great Britain. 1000-1902, by Frederick S. Hammond, Ryan & Burkhart Printers, Oneida, NY, 1902
[Note: Findagrave has the following: Parents: William & Mary Hammond of Melford, England; Thomas was baptized, with his brother John, in Melford, Suffolk Co., England, Sept. 2, 1603.]
