Purely by coincidence, I watched a eurowestern starring his colleague (and fellow Austrian) Freddy Quinn this morning, Freddy und das Lied der Prärie. I have never seen Alexander's western effort.
He was one of the most successful artists in the popular music genre in post-war Germany, along with the above-mentioned Freddy Quinn and (Italian born) Caterina Valente. Like Quinn he regularly appeared in movies, often sentimental Heimat movies or musicals. When the Karl May Movies proved to be an enormous success, it was no more than logical that Quinn and Alexander would appear in a western musical.
He usually wore a bowtie when appearing on stage