No you cannot dual mine zec, because it uses both GPU and memory. You can only dual mine effectivelly when one algo uses ONLY GPU and second ONLY memory. All in all, nvidia cards are not that good in dual mine, so it is usually very barely worth it.
um its always worth it, i get 29 mhs eth and 290 sia for 120. watt on 1070
also 29 mhs and 400 dcr,
if u dual mine its basically the same profits as zec most of the time
eth plus lbry would be real profit right now too