As for Sv. Vlaho, that isn't a Serbian name. "Vlaho" means "Vlach". It's also a very common name in many forms across the Balkans as a surname such as Vlasic in Croatia, Vlahovic in Bosnia, Vlahovski in Macedonia, and Vlahos in Greece.
The Serbs of Northwestern Bosnia have names that are entirely Croatian, such as Bilic. Vojislav Seselj is the only Serbian Seselj....all other Seseljs are Croatians.
Ave Diocletiane, te correcturus saluto.
1. The literature on forced conversion to Catholicism of Orthodox people is copious. Austria (Holy Roman Empire, Austrian Empire); Union of Brest-Litovsk for the Urainians, Maria Theresa for Slavonia. Not to speak of forced conversion of Protestants in the Counter-Reformation. Do your homework (Google or a library). A Sokac named JOVANCIC has an umnistakable base form JOVAN, Earlier Serbian and Croatian have IVAN, but JOVAN is (guess what).
2. VLAHO. Your folk etymology is charmingly innocent. There is no “Saint Vlach” in any church calendar, but only BLASIUS (Latin), Biagio (Italian) Blaz(h)(Croatian. Look up Blaise in any reference work when you reach the age of reason. Cf. Russian Vivliya, varvari: Latin Biblia, barbari... Or if you’re that insdolent:
http://www.nationmaster.com/encyclopedia/Saint-Blaise
Church of St. Blasius in Dubrovnik.
Blaise is the patron saint of the city of Dubrovnik (where he is known as Sveti Vlaho) and formerly the protector of the independent Republic of Ragusa. At Dubrovnik his feast is celebrated yearly on 3 February, when relics of the saint, his head, a bit of bone from his throat, his right hand and his left, are paraded in reliquaries. The festivities begin the previous day, Candlemas, when white doves are released. Chroniclers of Dubrovnik such as Rastic and Ranjina attribute his veneration there to a vision in 971 to warn the inhabitants of an impending attack by the Venetians, whose galleys had dropped anchor in Gruz and near Lokrum, ostensibly to resupply their water but furtively to spy out the city’s defenses. St. Blaise (Blasius) revealed their pernicious plan to Stojko, a canon of St. Stephen’s Cathedral. The Senate summoned Stojko, who told them in detail how St. Blaise had appeared before him as an old man with a long beard and a bishop’s mitre and staff. In this form the effigy of Blaise remained on Dubrovnik’s state seal and coinage until the Napoleonic era.
Bilic; Bijelic Belic; are dialect variants; etymology ‘whitey, blond’ or Sniješko Bijelic ‘snowman’. “Entirely Croatian” are only the dialects in which the neuter imterrogative pronoun is KAJ ‘what?” (e.g. in Zagreb, as well as in Slovenia) and CHA, on the islands). In Serbian that pronoun is SHTO (što). Except to chauvinist Croatianists it is unquestionable that literary Croatian is at base the west Serbian IJE variant of the SHTO dialect. Croatian Catholic Archbishop Strossmayer, the great Croatian linguist Ljudevit Gaj, and the Austrian Empire needed that to facilitate missionization of the people whose native language it was — the Orthodox Serbs. See the Vienna Language Agreement /Becki Književni Dogovor 1850).-Just consider the literary Croatian words: ISUS “Jesus”. Catholic Slavs (Poles, Czechs, Slovenes) use the medieval Latin form JESUS (Jesus, Jezus, Ježiš). One word for ‘wedding’ in (literary) Croatian is Vijenchanje’ - derived from Vijenac ‘wreath’ In the Orthodox wedding rite the priest places a wreath (crown) on the head of bride and groom. Not so in the Catholic ceremony.
Diocletian, get out of your palace once in a while and get thee to a library, or Google. You can learn something new every day.