Sounds like an interesting campaign. Have you taken into consideration the Great Migrations? What is the Earth-analog of the Sueloise and Oeridians in your setting?
These migrations are said to have moved from the west into the east to fill the Flanaess. With the Flan being the native inhabitants.
I guess when I see feudal medieval kingdoms I immediately want to apply European analogs. But your ideas are a creative way of thinking about it. I wouldn't even know how to begin applying an American ethnicity/culture to the Flanaess. I guess America is made up of several real-world cultures - the original Native Americans and the people who colonised it from Europe. In Greyhawk these colonists would be Oeridians and Sueloise, I guess, but what ethnicities/cultures are they in your setting?
1e Sueloise and Oeridians have some interesting ideas that moreorless work. But.
There are occasional cultural sensitivity issues with the presentation of the Sueloise and Oeridians, so I prefer a rethink for them. I would rather avoid the idea that these are two separate "races", and instead emphasize how almost every culture has arisen from ongoing local blends of multiple ethnicities since prehistoric times. There has never been such thing as "pure blood".
Generally, Gygax seems to have the two groups Sueloise and Oeridians parallel the British Empire and the Spanish Empire in the context of colonizing the Americas. This part is ok, tho requires sensitivity.
But then Gygax also seems to blend the Oeridians together with other "darker skin" Mediterranean groups including Islamic populations, even Asian Muslims, like Turkistan. In turn, Gygax has the Sueloese come across as if a "Germanic" race (which was never a single ethnic group in reallife). Gygax even approves Nazi assumptions of "purity". Meanwhile, he has those Sueloise in Hepmonaland become darkskinned to represent South American Indiginous cultures, in a kind of cultural appropriation. The racial assumptions behind the two groups Sueloise and Oeridians get offputting. Caution is necessary.
I prefer the Sueloise have nothing to do with the Vikings in the Corusk Peninsula nor the Indigenous in Hepmonaland. The Vikings come from lands around Jotnumheim Sea and maintain traderoutes with them and with Indigenous Flan.
It is probably ok if: Suel (geographically roughly the reallife Takla Makan Desert in Asia) was somehow a colony from Thalos (British Isles) or Lynn (France and Germany), which then migrated from the west into Flanaess (North America). Meanwhile, the descriptions of Oeridians seem to mostly correlate with the Tharquish Empire (Italy and Spain).