First of all, no you cannot get Electro Ball on an Electrike through the Dexnav because Electrike is not a Dexnav Pokemon.
To answer your question, yes all egg moves are available through the Dexnav as long as it is available by Dexnav. If you don't know what Pokemon are available by Dexnav look here.
>All Pokemon you can find in the wild are DexNav Pokemon. Just search them and you can sneak up on them. I just tried and I got an Elektrike with Electro Ball in about 5 minutes
I was thinking that the above Pokemon were the only Pokemon you can get by Dexnav, but you can get any wild Pokemon through Dexnav.
Sorry about that
Hope this helps!