Well, let's start with Arena and, in particular, Daggerfall (half of Daggerfall takes place in a section of High Rock, and it's a great example of Breton culture). Those games gave Bretons (mostly randomly generated) English-sounding names like Woodborne, or Bridwell, as well as a dash of classic fantasy names like Lysandus or Elysana. So, Anglican names (Irish, Scottish, English, and probably even Gaelic and Celtic) are lore accurate for Bretons. If I may guess at regional naming styles, I'd say that this was how Bretons of the Iliac Bay region were named, since that's how all of the Breton NPCs were named, no Frenchness. (and I don't remember any Mac- or Mc- prefixes to surnames, so maybe there's less Gaelic influence on the names than I'm granting)
From Morrowind on, most Bretons were given more French-sounding names. So, French-sounding names are also lore-accurate, and I'd guess that those Bretons hail from regions other than the Iliac Bay - perhaps central High Rock?
Then we have the Reachmen, who were introduced in Skyrim (and existed in the lore since I think Daggerfall!): tribes of witches and warlocks residing in the Reach of Skyrim and the Western Reach of High Rock. It's important to note that not all of the Reachmen are Forsworn. The Forsworn is simply a faction of native Bretons that violently rebel against the Nords; literally terrorists. There are a number of native Bretons in the Reach unaffiliated with the Forsworn, like Ainethach of Karthwasten, or Bothela and Muiri of "The Hag's Cure" in Markarth. They've all typically got names like Madanach, Ainethach, Kaie, Uaile, Braig, etc. The named Hagravens associated with the Forsworn are named Drascua, Petra, and Melka. Make of this what you will. I personally connect the names of some characters from Daggerfall (particularly Nulfaga, crazy old witch and mother to Lysandus) to the same style of names that the Reachmen have - it's probable that Nulfaga was associated with the Witchmen/women of the Reach. That would explain Lysandus's name, too, which falls more in line with the fantasy style of the Reachmen's names than any other real world anolog. I think.
Also keep in mind Breton, like Nord, has a meaning in the real world that's pretty blatantly connected to its Elder Scrolls meaning.