Good for them if the state allows it, but do you really want a state that doesn't follow it's own laws?

Switzerland is maybe the only country you have heard about that is pressing charges, but you have similar laws in the UK and Germany for example.

And if you read the article, both sides are concerned, they talk about someone who went too help the "DPR/LPR".

My first point still stands, this has still nothing to do with Russian money

This has nothing to do with Russian money, like most European countries, Switzerland has laws against serving in an other's country armies, especially when you did your military service in Switzerland