Actually, it’s a type of subordinate clause used as the object. In fact, your sentence is “complicated”, since it has a few embedded subordinate clauses. John wondered X. (X is the direct object of “John wondered”.) John wondered if the men felt X. (“if the men felt X” is a subordinate clause that is the object of “John wondered”. Such embedded yes-no questions are introduced with “if” or “whether”) (X is the direct object of “the men felt”). John wondered if the men THAT WERE being hoisted into the sky felt X. “that were being hoisted into the sky is a restrictive relative clause that identifies and gives information about the men John was referring to. John wondered if the men being hoisted into the sky felt X. In this version, “that were” is omitted, giving us a reduced relative clause. The meaning is the same, and it is good style to write clearly using as few words as possible. John wondered if the men being hoisted into the sky felt (THAT) the risk had been worth it. In this version, the direct object of “felt” is a subordinate clause “(that) the risk had been worth it.” Just like X, the clause functions as the direct object of “felt”. Using “that” to introduce such a clause is optional. If the meaning is clear without “that”, then it’s good style to omit it. On the other hand, if the clause were understood, we could replace it with “that”: “…the men… felt that.”

It will make sense if you add the word "that" after "felt".

I am not too strong on sentence structure and terminology, but I think it is the same structure as in: They thought {the risk had been worth it}. They thought {the house was too expensive}. He thought {Chinese was very difficult}. 他覺得{中文非常難}。 So "feel" functions in a similar way as "think" in this type of sentence. They can both be followed by a sentence {in braces in the examples} which is probably an object. And I think this sort of thing works in other languages too.

Yes, of course. Such as ; You are a nice person is a fake sentence. or, What I want to say u is u r cute.

Dear Rena, Your example was quite practical. Thank you for your clear explanation. : )