Is it considered a breach of an oath (hanth) if a person swore by divorce aloud not to play with his money, then decided to invest this money in commercial projects?

Divorce does not occur by mere intention or inner thoughts, nor by doubt concerning its utterance. As long as you are not certain that you pronounced an oath of divorce, do not pay attention to the doubt. If we assume that you swore by divorce not to gamble with money, then do not break your oath by trading with it, because that is not gambling.