All countries associated with the European Broacast Union can participate.
Theoretically yes, but associated members (in contrast to full members) still need to be approved on a case by case basis.
Active members (as opposed to associate members) of the European Broadcasting Union (EBU) are eligible to participate; [...]. Associate member broadcasters may be eligible to compete, dependent on approval by the contest's reference group.[49]
https://en.wikipedia.org/wiki/Eurovision_Song_Contest#Participation
1945 was 80 years ago. None of the people working at any german company today were even born when the Holocaust happened. I don't see how that topic is relevant when it comes to buying decisions today. Punish corporations for stuff that they actually can influence today, not for stuff that nobody alive is even responsible for.