Although I'm not a native speaker, in all of my years of experience, I've never seen they oughted to work harder. I don't think the past tense form of the verb ought even exists. Just like there's no past tense form of the modal must. I'd say that if you want to express ought in the past, you would simply say had. And to be perfectly honest, ought is not used that often in spoken English. You'll most likely hear it used as part of set phrases like you ought not judge, you ought not to have done that, et cetera. There's not a whole lot of expressions like that in English though.
PS: Notice that the grammar in the two examples with ought that I gave you is a little bit inconsistent. In the second example, there is a to while the first one doesn't have it. And that's the point that I'm trying to make: ought is an old-style verb that has survived in modern English in the form of idiomatic expressions whose grammatical structures may seem antiquated and irregular.