This is a complete fabrication. Never have I heard of this happening, let alone it being a major phenomenon anywhere.
Either the party worker has to be naive to believe that such ritual has any value or the people have to be completely stupid. Poor people are desperate and will happily take whatever money that comes their way and will not care too hoots about swearing on Gods. Remember if you can do a ritual to swear on God another one can invent a ritual to free you from that oath.
'Karnataka election 2018: Rider for freebies - swear in the name of god that you'd vote for me'[1]
[1]:https://m.timesofindia.com/city/bengaluru/karnataka-election...
While there certainly is corruption, given the size and scale of elections in India, it is laudable that things are conducted in a proper manner for the large part.