Long story short, no, they are not related. Latin nebula 'cloud', nubes 'cloud', (related to German Nebel 'fog' and the source of English nebulous) < PIE *nebhes (A-H and IEW), and Latin nubilis 'of marriagible age', nubo 'marry', < PIE *sneubh- (IEW).

Ceci n'est pas un seing.