By class traitor I don't mean a fed or infiltrator. You don't have to go out of your way to denounce leftist ideas or stop the left. You just have to have class interests directly in conflict with workers and the poor. You can let your factory unionize, and take less money. But would you choose to be that factory owner if it meant your current situation improved significantly?
I don't know what I would choose because I have no hopes of owning capital. I would love to quit my job and be free to just own stuff and make money off it. But then I would have to reckon that with my beliefs. I guess you could just accept you can't be a leftist and volunteer for the wall should the day come.
I think the morality of an action should be primarily determined by the expected real world material consequences of said action, either positive or negative. Doing anything just for the sake of purity is silly, and can often itself be immoral if the outcome would have likely had a positive impact otherwise. Related to your question, it depends. Would you be directly making someone's situation worse? In that case, it would obviously be bad. Would a specific act of participation in capitalism benefit you or people/groups you care about while having an inconsequential impact on the capitalist system as a whole? (making money from stocks might be an example of this) Then it might be worth it to take advantage. You'd have to look at each situation independently and weigh the benefits and drawbacks. Also, as far as the argument around class loyalty goes, I think it really will be socialism or barbarism no matter how financially secure you think you are, so you should support the overthrow of capitalism no matter what.