In English, 'Are you married now?' and 'Are you now married?' has the same meaning and hence both should be accepted.
Technically correct, but you'd never hear a native speaker use the latter.
I thought I could leave out the second person pronoun (te)?
In the interrogative form, does the subject pronoun need to be included? "Oletteko nyt naimisissa" was marked as incorrect for me.
No, "oletteko nyt naimisissa?" is a perfectly fine question. But if the task was to translate the Finnish sentence into English then it wouldn't really work, pronoun or no. :)