It is accepted.

He has not considered the fact that some nouns in English you'd refer to as "it", while in Czech they are masculine (and it works similarly also for neuter nouns).

She is looking at the house. -> She is looking at it.

Ona se dívá na ten dům. -> Ona se dívá na něj.

We may all need to consider the possibility that your husband is wrong.

First, let's compare these three tables, this one, this one, and this one. They are the personal pronoun declensions for masculine animate, masculine inanimate, and neuter genders. You will find "něj" in all three tables for "4. pád" and "jednotné číslo", or the accusative singular. This should convince even casual observers that "něj" is applicable to more than just the masculine gender pronouns, namely to the neuter pronoun "ono". (You did not quite say that your husband claimed "něj" is only masculine, but the alternative to that assumption would be that "něj" is not applicable to anything at all, so that is why I addressed it.)

Now we need to consider the challenging fact that the English "it" can correspond both to one of the forms of the demonstrative "to" and to a form of the personal "ono" in Czech, depending on what we are doing or which English "it" we are dealing with. A blanket statement like "you can never translate it as něj" is so sweeping that it should raise red flags immediately. How much thinking did he put into making it? "Ono" is rare in the nominative, but much more common in other cases.

Some people only respond to examples. Here's mine; others are under the third table I linked above.

Say we are talking about looking at a car. That verb object, "auto", is neuter even in Czech. I would challenge everyone to tell me whether it is really more appropriate to use TO than NĚJ in the following exchange:

• Did you look at the car yet? She is looking at it.
• Už jste se dívali na to auto? Ona se na [něj/to] dívá.

If you stuck TO in that answer, it would be rather disjointed, similar to answering "She is looking at that." At what? Do you mean the car or some other thing? This confusing level of reference disconnect is similar to what you often get from using the wrong article in English. Not only can this "it" be translated as "něj", but it cannot properly be translated as "to".

As far as the "ono" forms applicable to the singular accusative with a preposition, there are two shown in the table, "něj" and "ně". Of the two, "něj" is more common and is more useful to foreign learners because it overlaps with the masculine, so they get more bang for the buck. A lot more about that angle here.

Unfortunately it is always easier to make misguided assertions, even if they are made in good faith, then to fix them. I hope this helps someone.

This is a GUESS, since I don't know what the whole sentence was (and I am learning, too).

If you got this as a Write This in Czech exercise, and if your answer started out with "Ona dívá se....", it would probably have been considered incorrect because of the placement of "se," which generally wants to be in the second position. If you had written "Ona se dívá...", I think it would have been correct, assuming DL didn't find something else that it didn't like in the sentence.

I think that your version would be "I am not looking at HIM," while the word in the Czech sentence is "IT."

This is quite a specific wording. You must strongly stress eith NA NĚJ or DÍVÁ and the meaning depends on that. But we accept a very similar one, so I will add it.

No. You use něj instead of jej after prepositions.

The hints are only hints. They work like a dictionary, they list many possible translations of that word but normally some of them cannot be used in the current sentence.

Here jej is use without prepositions and něj is used after a preposition, please read also our Tips and notes.

His v zadnem pripade. Mohlo by tam byt, a uznavame, HIM.

Ale pokud se diva na hrad, na stroj, na stul. Tak v AJ to je IT. V CJ je to něj...