Here in Italy it is not a common name, I know only one person named Santo and to me it sounds a little strange, but you can get used to it. It helps that actually you rarely use the word "Santo" near a saint's name, it's more common using "san" (san Michele, san Pietro). Also I want to underline that in Italian Santo is not connected to Santa Claus at all. Santa Claus is Babbo Natale, so totally different; also Santa Claus derives from Saint Nikolaus, not a Saint named Claus.
I think Santa Claus should be the name of Mrs Claus and his name should be Santo Claus because it's masculine and Santa is feminine. The person who named Santa obviously wasn't all that bright. And they're Italian.
Santo in other languages is a surname of religious inspiration, more precisely related to Christian identity when he speaks of someone who is devout or blessed. For example, in the Italian language, there are forms Santi, Sancte, Sante, Santé, Santese, Santes, Santy, Santesi, Santhia, Santia, Santis, Di Santis, De Santis, De Sanctis, Desantis, Sanctis, Di Sanctis, Sancti, Di Sancti, Sanctius, Sancto, Di Sancto, Dei Santi, Santini, Santinni, Ognissanti and Ognisanti (then Santi is son of Santo or in English is Descendant of the Saint man / the Just man / the Righteous man). It's a household name in the North of Italy (Cisalpine Gaul) where from Celtic tribes from Ireland and Scotland were established or settled for centuries in Northern Italy, especially in Piedmont. One of the best known cases is the Scotti surname and it comes from Scott (Scottish; a native of Scotland or born in Scotland) that comes from the Scottish Gaelic. Then Scott adapted to the Italian language and added a Latin I representing a suffix of sonship. That is, the descendants of Scott.
https://www.behindthename.com/name/santo/top/brazil
https://pt.m.wiktionary.org/wiki/Santo