The first part of "Cachet" seems to be pronounced similar to "Cacher" though "Cacher" seems to be pronounced similarly to the accute "é" at the end. Thus, they're not homophones but they're extremely similar. "Cachet" means "official" or "signed". Interestingly, "Cacher" which is spelt and pronounced identically is also the French verb for "hide". Thus, the French word for kosher, hiding/concealing, and "Cachet" are all nearly identical.
Varg claimed in his genealogy video that the name comes from the Letres de Cachet given to a count by the king of France along with some land to perform "some duty", and later on one of them was executed during the French revolution. What was this duty? I found some records of a "Cachet de Montezan" from before the revolution, specifically another Louis Cachet ("Louis" seems to be a common name in this family, thus could it be said that the Cachets have wholly infiltrated Varg?). He built a canal from Lyon through La Dombes for commerce. It doesn't specify that he was a merchant however, so red flags for him seem to end there.
There's this French book on Amazon that apparently details the histories of the Cachets, written by a Cachet himself, "Eudoxe De Lombardon-Montezan". https://www.amazon.com/Souvenirs-LAncienne-Principaute-Montezan-Litterature/dp/2012591426
Their coat of arms (apparently multiple for the same name, which is odd in itself) are also detailed on this website. Also of the Cachet de Garneran, which seem to be the same family (just as the counts of Garneran, and not of Montezan): http://www.coats-of-arms-heraldry.com/armoriaux/rietstap/blasons_CAAN_CAES.html>Supporters: two addorsed lions facing the sinister heads. >Gules, 3 pales Or, charged each one in chief of a lozenge Sable.
More books, specifically their origin as the counts of Garneran, and later "Lombardon" (Lombards from northern Italy): https://www.abebooks.fr/rechercher-livre/auteur/de-lombardon-montezan/
This essay lists "Comte Louis Cachet de Montezan" as the noble envoy in Munich during the revolution:https://quod.lib.umich.edu/w/wsfh/0642292.0032.007/--courtesans-of-the-king-diplomats-and-the-french-revolution?rgn=main;view=fulltext
Most oddly enough, Polish Wikipedia has an incredibly short article on the original Louis Cachet, citing French books. https://pl.wikipedia.org/wiki/Louis_Cachet_de_Mont%C3%A9zan>Louis Cachet, Count de Montezan - a French military officer, high civil servant and diplomat who lived in the 18th century.>In the French army he became a cavalry captain. In the years 1730–1747 he was the president of the parliament in Dombes, as mentioned in the Encyclopedia of Diderot and D'Alembert. He later served as authorizing officer for Dombes. Being him, he ordered in 1758 to dig a communication channel in Thoissey (Saona River).>In later years he held diplomatic functions. In the years 1777–1779 he was the minister minister in the Archbishopric-Cologne Electorate, and in the years 1780–1789 in the Bavarian Electorate (Munich).
So Polish Wikipedia talks about the Cachets, but English and even French Wikipedia don't? He was apparently a high-ranking military officer alongside all what was said before, such as him ruling the Dombes and making a canal, and being the diplomat to Bavaria. I don't really see any smoking-gun evidence of him being directly jewish however, aside from linking him to the old lines of France including the jewish kings of Septimania, and dukes of Aquitane and Normandy,