When I was a kid several of my friends' parents (who were less
ambivalent about being Jewish than my parents were) had albums by
Richard Tucker and Robert Merrill in their collections. I Googled
"Jewish opera singers" because I couldn't remember Robert Merrill's
name, and to my surprise the name Kitty Carlisle also came up. I
remember her from that game show "To Tell The Truth," but I did not know
she was an opera singer, or that she was Jewish.
As for Elvis, did he know at that point in his life that one of his
great-grandmothers was Jewish? If so that might explain why he was
curious about cantorial singing. I mean, if you haven't grown up hearing
it, it's going to sound really weird and foreign to you...kind of like
how Chinese opera sounds to me.