ought as auxiliary verb.Ought is an auxiliary verb that usually takes to with its accompanying verb: We ought to go. Sometimes the accompanying verb is dropped if the meaning is clear: Should we begin soon? Yes, we ought to. In questions and negative sentences, especially those with contractions, to is also sometimes omitted: We ought not be afraid of the risks involved. Oughtn’t we be going soon? This omission of to, however, is not common in written English. Like must and auxiliary need, ought to does not change to show past tense: He said we ought to get moving along.
So if it's being used in a formal, written context, then yes. Otherwise, you decide. I tell my students however that if they wanna sound natural, then they oughta just say "should."
Well, I can only speak for my region, but using "ought to" in a non-formal, though not necessarily informal, setting is sure to cause a strange feeling in those speaking with you. Whether this is true outside of the American southwest, I don't know. Admittedly, I have nothing to back this up with other than my experience.
So, when I say "natural" I mean, "in an ordinary, non-formal context."