In chimps--our closest relatives--food hoarding is a well known privilege of rank.  Chimps will share many things, but as adults they do not share food with other adults (Bonobos, who inhabit a food rich environment, being a possible exception).  More likely than any indication that there is some sort of hard-wired fairness concept at play, the outrage showed by the Capuchin is evidence of a hard-wired feature related to resource control/capture.  Its impossible to tell, but the outraged Capuchin looks like it might be the larger of the two.  Capuchins are very aggressive and notorious for stealing food.  (I suspect the outrage would be greater in an individual on the alpha end of the dominance spectrum and more subdued on the omega end.)  A universal tendency towards fairness would be nice, but its unlikely except as a strategy in which the cost/benefit (measured across the species) is a net positive (which is what biologists assume is the driver behind the human tendency towards altruistic behavior).

The research subject makes this video interesting. The wealthy seemingly all white audience laughing at a captive monkey who vehemently and emotively rejects inequality is what takes it to the next level.

It reveals an inherent sense of fairness, suggesting that social justice may not be a silly fantasy, but quite natural indeed.

Do you really want to endorse the general principle that whatever is agreeable to monkeys should be endorsed among humans?  I think that strategy will take you places you don't want to go.  (Rape and infanticide are routine among monkeys; those instincts no less natural than their sense of fairness in food allocation).

The problems in reasoning from purely descriptive facts about the natural world (let alone facts about monkeys!) to normative conclusions were first identified by Hume centuries ago.  It's one of the most important insights of modern moral philosophy, and perhaps something a sociologist would find worthwhile to think about.

I would like to see a continuation of this study in which one monkey is given more than one piece of cucumber to determine if it is merely a food valuation issue (in that one piece of cucumber is not worth the same as one grape) or if it is the desire for the same reward.

If there is an equivalent value of cucumber to grapes it could be shown to be equal treatment, but if it is that only the grape is now desired, it would be more on the sense of envy and selfishness than equality.

I wouldn't accept a substandard reward for the same task, but I might accept  a larger quantity of a substandard reward vs a smaller quantity of a higher quality reward as they could be considered equivalent in value.

Equal pay for equal productivity isn't something you'd find many people disagreeing with. In fact, I'd say that that concept of fairness is the position of the people most strongly against modern concepts of social justice.

Not to say that there isn't a fairness principle, but this clip doesn't support that interpretation. Maybe this is just part of a whole series of studies supporting a fairness principle, but all I see is a monkey observing that a more desirable prize exists and expressing displeasure with the less-desirable prize. This could easily happen without the other monkey being there at all. Wouldn't the monkey probably have a very similar response if the researcher simply revealed that grapes were also in the treat basket?