The only ethnic listing for Sizemore has been Sephardic jewish. They were this and are this before there was native indian blood mixed. In Jamestown the only Sizemore was listed as a Sephardic jewish slave. In barbados they were listed as portuguese Jews. Read the articles below. Look for John and richard Sisemore who owned land in Barbados

Barbados Link to Melungeon Surnames
Melungeon ancestry possibilities have expanded to include significant numbers of "English" and "Scotch" settlers who came to South Carolina in the late 1600s and early 1700s,
but not from England. Although these people held English citizenship, their actual ethnic make-up was far different from the prototype Anglos of that period. These settlers were from Barbados, ethnically mixed people seeking better lives in the mainland colonies.

These so-called "freedmen" tended to be a mixture of English and Scotch, native Barbadians (i.e. Indian), Portuguese Jews, other Mediterranean people, and Africans. And,
most telling, their surnames match those English names that most commonly show up among the earliest Melungeon populations. It would seem likely that, over time, these ethnically mixed "Englishmen" would have indeed moved northward and admixed with Melungeon ancestral groups in the Carolinas and Virginia. There are many related documents detailing the movements of these early settlers, but one will suffice for this first announcement (this document kindly provided by Angela Andrews of the University of Virginia). John Camden Hotten's work on the Barbados settlers provides the following astonishing surname list of "English" settlers from Barbados: (see below for Library of Congress citations)

Freedman
Clark
Hall
Kennedy
Phipps

Portuguese Jews
Atkins
Cole
Isham
Miner
Sizemore

Look for sisemore below
This List, which is reprinted in P.F. Campbell's "Some Early Barbadian History", published Barbados, 1993, appears to be part of an old publication which Campbell reproduces in its entirety, and which is entitled: "Memoirs of the First Settlement of the Island of Barbados and other the Carribbee Islands, with the Succession of the Governors and Commanders in Chief of Barbados to the Year 1742, extracted from Ancient Records, Papers and Accounts taken from Mr. William Arnold, Mr. Samuel Bulkly, and Mr. John Summers, some of the First Settlers, the last of whom was alive in 1688, aged 82. Also some Remarks on the Laws and Constitution of Barbados." by William DUKE, the clerk of the House of Assembly, who first published the 100 page book in Barbados in 1741.

Second edition London 1743. Reprinted in Bdos 1891. For more details, see Handler's "Guide to Source Materials for the study of Barbados History", page 30.London, Printed for E. Owen near Chancery Lane, Holborn, MDCCXLII.

LIST OF THE NAMES of the Inhabitants of Barbados, in the Year 1638 who then possess'd more than ten Acres of Land.
Stallange Roger
Stirring George
Stringer John
Sandiford William
Secretarie Mr.
Sisemore Richard
Sisemore John
Stokes John
Smith William
Sawer Richard
they were regesterd as Portuguese jews!!! It is documented!
many Sizemores intermarried other Jewish families in America! the greens,coopers,shepards,blevins and Moselys
Some mixed with native indians some did not But originally they were Sephardic Jews before they came to America!