I see two things here. The first is that I am surprised that there are a lot of states in the USA where gambling is not legalised. Gambling has its bad things, like alcohol for example, but it is more than proven that by prohibiting it you don't eliminate it, you leave it in the hands of mafias and you stop collecting taxes. And this brings me to the second part, that part of the taxes will be used to help the homeless seems to me to be a poor argument. What we have to do is to attack the root of the problem and try to avoid, or at least reduce the percentage of homeless people.
Then, as for the clothes that people may be wearing, I consider that a secondary issue.
Gambling houses will do whatever they could to gather people in their favor, even if the means they employ to reach is that is of poor taste. To be honest I don't think it would work with the people. The fact that it insinuates that gambling does good is already a flawed concept, let alone that the taxes they incur are being paid to fight homelessness. We take a look at everywhere and it doesn't seem like actions against homelessness is being taken to alleviate it, let alone to completely eradicate the tragedy. This advertisement, if true, is done in poor taste and should be a lesson to every gambling company out there not to.
You also have a point in attacking the homelessness tragedy but without the primary proprietary entities to handle the issue, there wouldn't be an end to people lying in cardboard boxes in the streets. The government needs to be urged, or we could just leave it to the NGOs and watch it gloriously fail because they lack the proper funding.