Wow...didn't think the response to this initial question would be that large.
Yeah it is more a legal issue, really than an ethical one. The law is pretty explicit, ANY medium of exchange is illegal under the FEDERAL law that re-legalized homebrewing 40 years after prohibition was repealed.
Homebrewing and money is such a sticky situation, homebrewing and the law is a sticky situation. I mean it's still illegal in Alabama, and Utah only legalized it a couple years ago. And even a lot of state laws are screwed up in terms of if you legally can enter contests, or even drive your beer to a public place for a homebrew club meeting. Or if you can hold a homebrew contest in a bar where legal and taxed alcohol is sold (these are all actually issues that have come up over the last few years in this hobby. You can find news stories about all of these on this site.)
Technically you might be crossing a legal line if you then gave them beer made with the ingredients- maybe not if you served them a beer in a social situation, but if you dropped of a sixer of each batch to them. One could say there was an illegal monetary exchange for that beer.
Whether or not it would be legally pursued is another matter, but I'm always uncomfortable even with folks discussing this online, you really don't know what or who's watching the largest hobby alcohol producing website on the planet at any given time. Or if there's keyword bots looking for conversations like this.
Personally I staunchly avoid any situation like this. If anyone asks or offers me money, I simply thank them but say it's illegal.
For me it's about respecting the battle that was fought to get the hobby legalized and about how much this hobby is misunderstood by many folks as someting quasi legal or dangerous anyway. So I tend to step lightly around this.