No. It is a mistake to think of it as "hello" and we want to discourage that mind set. nuqneH does not mean "hello" in Klingon society. It still means "What do you want?" For instance you should not use it when you walk up to a Klingon and want to be polite about your arrival. You also should not use it when you want to get a Klingon's attention because he is busy and does not seem to have noticed you (trust me, he did and he's ignoring you). The perfect time to use it is when a Klingon has walked up to you, but then just stares at you or seems to be evaluating you rather than stating his business. Then it is perfectly appropriate to say nuqneH "What do you want?" But that's a far cry from "hello".
It's not wrong, in principle.
But remember that alternative translations have to be added by hand, since Duolingo doesn't actually understand Klingon.
So in general, it's better to stick to the order of the original sentence where that makes sense, as those will be more likely to be in the system already -- whichever of us added a sentence may or may not have thought of other orders or have had the time to add alternative orders.
I'll double check what we said, but I think you have taken that statement too broadly. The English Subject Verb Object order is reversed to Object Verb Subject, but it's not true that everything is reversed. Some parts of Klingon grammar are in the same order as English. You can't just take an entire sentence and reverse it. And what about a paragraph? Don't start reading the paragraph from the end. You still have to read it one sentence at a time from the start. In a case like this where Mara's name is being called and is not actually part of the exclamation, then when her name is before the exclamation, it should stay before the exclamation and when it is after the exclamation, it should stay after the exclamation.