It is true that the German Umlauts ä, ü. ö are transformed to ae, oe, ue to compensate for systems, languages, codepages etc. not supporting those. But do not take this as a general rule for every appearance of a German Umlaut just like the example of the artist real name "Lutz Roeder" shows. There exist a lot of German words and names which indeed use ae, oe, ue instead of German Umlauts.