So to be upfront, we have exactly 0 examples of Norse figures who converted to Buddhism. Hvitserk himself is an attested figure from several literary sources, and some scholars have claimed that he is the same person as Halfdan Ragnarrson mentioned in some other sources, most of which however are not contemporary to the events that they describe. None of these sources mention a conversion to Buddhism it must be said, they do mention his campaigns in Northern England and Ireland and his eventual death at the hands of the Irish.

So that's the answer as it relates to Halfdan specifically, but what was the larger Norse relationship with areas of Buddhist influence such as China and India? There actually is something to base this off of, on the Swedish island of Helgo (Helgoe? idk how to anglicize Swedish umlauts), a small Buddhist statuette was unearthed. Its provenance is uncertain, at least for the English sources I looked at, I imagine there's some Swedish source that spells it out in Academic language, but I don't read Swedish...

So there is a connection, likely trade, that carried this artifact from modern day India/Pakistan to Scandinavia. Now its unlikely that Buddhists (or vikings) were the ones who carried it all the way, or that it was done all in one trip. The trade routes across the Norse, and Byzantine, and Islamic world were filled with intermediary groups, and while Norse traders from Sweden or Russia might go down into the Caspian or Black sea, its unlikely they'd make it all the way to the Indus. More likely the statuette was transported through various intermediaries before it ended up in Sweden. Now as to why it ended up there, that is unfortunately impossible to really tell, but the site it was found on is a known trading area that included artifacts from across the Norse world and its trade network.

Now the second part of your question, how did the Norse treat religious minorities within their sphere of influence? Its a good question, but difficult to answer. Many of our sources about pagan Scandinavia come from the hagiographies of Saints, including martyrs, and these sources are keen to play up the barbaric cruelty with which the pagans treated their Christian (and really Christians are the only minorities we have evidence for) populations. There is certainly evidence of continued Christian populations in the Viking world, likely having to do with influence from Christian traders from Frisia, Saxony, and England, as well as any communities that missionaries were able to make head way in. Over time the Scandinavian kingdoms would convert, though only after the ruling class (especially kings) converted, starting in the 9th century.