From this statement found in the Brief History of Eastern Oerik (p. 5) we are made to understand that the people of the Hold of the Sea Princes are not racially intermixed--or at least not of Suel-Oeridian mixture--but of which stock are they? Suel, Oerid, or another race entirely?
Given the Hold's close proximity to the former grounds of the Suel empire and that slavery is practiced in this land,* it would seem a rather safe bet that the Hold is comprised of a predominantly Suel population. Furthermore, the Sea Princes are described as the strongest naval force of the region, and have a long history of piracy and other maritime activity--hence their name. As the historically landlocked Oerid peoples are described as being "indifferent sailors," only taking to the sea when the Great Kingdom sought to expand to the Islands off its eastern shores, the evidence clearly favors a Suel occupation over an Oerid one.
Contradicting this, however, is the map of migrations (right) which clearly shows that both the Suel and Oerid peoples managed to find their way to the lands of the Hold.
Furthermore, A Guide to the World of Greyhawk Volume III--the later edition of the Gazetteer published in 1983--includes a table which uses a symbology of letters to indicate the racial mixture of various regions of the Flannaes. The entry for the Hold reads thusly:
"Sea Princes -- SOf"This encryption indicates that the people of the Hold are comprised of a heavy mixture of Suel and Oerid peoples, with a bit of Flan thrown in for good measure. Which is to say, the Hold is no different in its racial make up than the rest of the Sheldomar Basin; so why did it get called-out in the Brief History as being somehow distinct from the rest? A rational mind would say that the author either thought better of the notion of racial purity in the Hold, or forgot that he'd ever mentioned it at all. An irrational mind would link this oversight to the human skull in the crayfish encounter in T1. I always prefer the latter approach but haven't come up with anything good yet.
*Greyhawk enthusiasts will know that the Suel people were the sole practitioners of slavery in all of Oerik. Bastards.