The man page for configure-proxy.sh says to use either 1 or 0 for USE_SSL, but the yes_no function in configure-proxy.sh will convert this back to 0 (only values Y|y|Y/n|n/Y will end up as 1). Either the man page or the yes_no function needs updating.
1 is taken up as Y now. Commit b08e741d965535d9d67cb61abbd0200d6fa936e9 Fixed in spacewalk-proxy-installer-0.6.20-1
Spacewalk 0.6 released.