Yes, they are people trying to make a buck. No, they are not employed
by the town. As for "too much effort for minimal reward," it's
difficult for you to make that judgment, considering that (a) you have
no idea how poor they are, (b) you have no idea how much they manage to
make by collecting cans and bottles, and (c) you may not understand
their work ethic, if they are from a foreign country (as you've
indicated) with a culture that is markedly different from ours. Also,
considering that they are probably not employed, then spending time
collecting cans and bottles is more profitable than whatever else they
might be doing, regardless of how much they actually make from it.

As for the glass bottles, they may take them to recycling centers which
pay money for glass, or they may wash them out and use them at home, or
they may wash them out and sell them.

An anecdote to lend some perspective.... I recently heard a guy on NPR
talk about how when he lived in India, his trash was picked through by
multiple people before the collectors ever got to it, such that very
little of what he put out was left for the collectors. He said that
each person to go through the trash was of a lower caste than the prior
person -- there was actually an organized hierarchy of who was allowed
to pick through which trash when.