Wikipedia seems to agree with you here (
http://en.wikipedia.org/wiki/Joanna), but it's uncited. I can't find any other sources that back this, but it makes more sense to me that if Yochanah was in use back then, it may well have been as a male name. Also, if it's used on female Hebrew speakers today, it is probably derived from
Johanna and not the other way around. So, as long as there aren't sources that confirm that theory, I wouldn't add it to the database.
Joshana doesn't make sense because the Hebrew form of
Hosanna is hosha na (with a heh). Hehs aren't anglicized into J's, yuds are.
I think Nissiah does make sense syntactically as a made up name.