In another question, a reference was given to Varro:
De subus nemini ignotum, nisi qui apros non putat sues vocari.
which was translated as:
As to swine, everybody knows — except those who think that wild boars ought not to be called swine.
At first, it simply struck me as an odd translation. Reading the Latin I got the impression that Varro is referring to a specific person even mocking him a little. Influenced by a recent reading about est/sunt qui constructions, in which the verb inside the clause is usually in the subjunctive case, thus producing a relative clause of characteristic (some examples in A&G 535.1); however the construction sunt/est qui can also come with the indicative. A good take on that can be found in a note on Horace Odes 1:3 (sunt quos curriculo pulverem Olympicum ...):
Sunt quos] The Greeks say ἔστιν οὕς. The indicative is used with ‘sunt,’ or ‘est qui,’ when particular persons are alluded to, as here the Greeks in opposition to the Romans. So Epp. ii. 2. 182: “Argentum — sunt qui non habeant, est qui non curat habere,” where, by the latter, is distinctly indicated the wise man. Here Horace alludes to the Greeks of former days, and is led to refer to them, because this was the chief subject of Pindar’s poetry.
I expected a specific person Varro is referring to because he used the indicative inside the clause. However, this is clearly wrong since it seems that usually nemo aliquid facit nisi qui comes with the indicative (while the simple nemo est qui usually comes with the subjunctive).
That leads me to questions:
What is the difference between the subjunctive and indicative inside the nemo alquid facit nisi qui clause. Is it the case it must agree with the mood of the verb of nemo?
Is it possible to use this construction to refer to specific/particular persons that are exception to the nemo?