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I have not made that recipe, but I have it out and am looking it over. This is your basic Austrian Sauerkraut 101 and it is a very authentic recipe, especially the absolutely essential soak and rinsing of the sauerkraut to start with. However, an Austrian would cook the bacon to render the fat, then use that in place of the butter.
The Schnapps is optional, and you probably wouldn't even miss it with the other ingredients, apples, and Riesling.
Apple schnapps is not a sweet liqueur. It is a distilled clear eau de vie and has very little apple taste. A suitable sub would be Calvados or Applejack if you have either of those, if not, a splash of cognac or brandy will stand in just fine.
And to be true to the recipe, you should use a German or Alsatian Riesling. The American Rieslings taste nothing like the German ones.
Enjoy!