I checked, that should work. Oliebollenmix contains a bit more than just flour and yeast (https://www.ah.nl/producten/product/wi4342/koopmans-mix-voor-oliebollen has a bit of salt and sugar too, and some potato/grain starch)... I could ask my mother about her recipe for oliebollen, she makes them without mix too, and see how it differs if you'd like :)
But making the batter, then following the first link should probably work. The end result might be much 'drier' though, as oliebollen are greasy things.