No error message if DM device <name> exists but it is not LUKS device.
dmsetup create x --table "0 100000 zero"
echo a | src/cryptsetup luksOpen /dev/sdc x ; echo $?
1
but
dmsetup remove x
echo a | src/cryptsetup luksOpen /dev/sdc x ; echo $?
0
echo a | src/cryptsetup luksOpen /dev/sdc x ; echo $?
Device x already exists.
5