You're really assuming that you know a lot about person C without ever meeting him/her. It's really easy to do that when you're just making it up.
The bottom line is that the hipster (aka Person C) is not going to employ the homeless. They are not going to fork over money out of their pocket, or create a positive sum job. Because it's hard. Instead they carp on the sidelines about "exploitation" (what does that even mean?) rather than stepping up and doing something themselves.
I really don't get the use of "exploitation" here. I guess the unarticulated concept is that these people are poor, and have no skills, and thus no leverage with which to negotiate for high pay...so it's "exploitative" to pay them anything, or anything below minimum wage, or anything below a software engineer's per diem?
This concept refuses to engage the fact that for a business to stay afloat, one's pay is upper bounded by the profit produced. There is no obvious business model by which a homeless guy with no skills is going to produce $80k/year of value. But there is some possibility that they can produce $20/day, or $7k/year of value.
The hipster will attack a hotspot job as exploitative, they will attack a minimum-wage "McJob" as exploitative, they will even attack the conditions that software engineers at EA voluntarily tolerate as exploitative. In fact, they will do everything other than step up to personally show just how it is possible to profitably employ someone at B's skill level without being "exploitative".
Minimum wage laws are an anti-market baseline, just like statutory rape laws. We use them both to set a general civil upper bound on the level of exploitation.
But make no mistake about it - it's a stunt. These homeless people get a tiny amount of money for a tiny amount of time. There's no real meaningful difference made to their lives. A few people get to meet homeless people and that's great, reduces stigma and promotes social inclusion. But did any of those homeless people go on to get jobs?
In general, when you're dealing with a population with large amounts of mental illness, substance misuse, victims of violence, etc you should be extra careful to provide proper support.
Like I say, this group appears to have done okay, and some of the people complaining are doing it wrong, but they could have done it better.
But the thing is that the people criticizing are (a) providing zero direct support to the homeless and (b) not actually going to "do it better". Few of the people offended by this whipped out their own $50 or $500 and said that they'd pay the homeless guy that much to do something else.
That is the point: few of the critics are actually capable of "doing it better" or would be able to withstand the media spotlight that would accompany an attempt.
I am.
But I did say that many people are too quick to complain. (I appreciate my wording was not good.)
Even still, lots of people choose freely to work for less than the minimum wage. They work on startups.
(1) Not as hard as one of these job things anyway.