True! Years ago there was a prominent cricketer who was known as Lorrie Wilmott; it turned out that his given name was not Lawrence as might have been imagined but Lorraine; it was a name commemorating warfare, and only connected with the fem. name in that way. Something of a 'Boy Named Sue' situation ... and South Africans are notoriously bad at French.
So Valmay/Valmae/Valmy could well go that far back: another thing that South Africans do is use family names for generations. But ... our links with France go back to the Huguenots, who rapidly became assimilated, so we'd have to assume a very politically alert naming population at work in the 1790s. Generally speaking, of course, Afrikaans South Africans would have tended to support France, the Batavian Republic etc against England ... but only once England had become a colonial power here, which was in 1802 for the first time. I really doubt whether monarchy mattered to them at that time, especially someone else's! Their subsequent republican stance was basically part of their anti-Englishness: they didn't mind the Dutch monarchy at all, or the Kaiser!
Are there any instances of Valmay/Valmae/Valmy being used as a given name elsewhere in the English-speaking world? It would be interesting to know.
My sister-in-law was named Valerie in the early 1940s, but her parents dithered between Valerie and Valmae for her; clearly they liked Val as a nickname and weren't sure which 'long' form of it they preferred. It was just a question of the sound of the name; no connections at all.
This has been really interesting: thanks to you and Lumia.